Chapter 22 - Skin Infections (Nov. 25, 2025)

Staphylococcus aureus

A Gram‑positive bacterium that grows in clusters resembling grapes and is commonly found on the skin and in the nasal passages of humans. While it often exists harmlessly as part of the normal flora, it can cause a wide range of infections, from minor skin conditions like boils and impetigo to serious illnesses such as pneumonia, sepsis, and endocarditis. Its virulence is enhanced by toxins and enzymes, including Protein A and coagulase, which help it evade immune defenses. Some strains, notably methicillin‑resistant Staphylococcus aureus (MRSA), pose significant challenges due to antibiotic resistance, making it a major concern in both healthcare and community settings.

Coagulase

An enzyme produced by certain bacteria, most notably Staphylococcus aureus, that causes blood plasma to clot by converting fibrinogen to fibrin. The coagulase test is commonly used in microbiology to differentiate coagulase-positive S. aureus from coagulase-negative staphylococcal species. Coagulase activity is considered a marker of virulence because it helps bacteria evade immune defenses by forming protective clots around themselves.

Protein A

A surface protein produced by Staphylococcus aureus that binds strongly to the Fc region of immunoglobulin G (IgG) antibodies. This interaction disrupts normal immune functions such as opsonization and phagocytosis, helping the bacterium evade host defenses. In addition to its role as a virulence factor, Protein A is widely used in laboratory research, particularly in antibody purification and detection, because of its high affinity for IgG.

Hyaluronidase

An enzyme that breaks down hyaluronic acid, a major component of connective tissue that helps hold cells together. By degrading this substance, hyaluronidase increases tissue permeability and facilitates the spread of fluids or pathogens through the body. In medicine, it is used to enhance the absorption and dispersion of injected drugs, while in bacteria like Staphylococcus aureus, it acts as a virulence factor that helps the organism invade host tissues.

Collagenase

An enzyme that breaks down collagen, the main structural protein in connective tissues such as skin, tendons, and cartilage. By cleaving peptide bonds within collagen fibers, it plays a role in normal processes like tissue remodeling and wound healing, but can also be produced by certain bacteria (e.g., Clostridium perfringens) as a virulence factor to help them spread through host tissues. In medicine, purified collagenase is used therapeutically, for example in treating Dupuytren’s contracture or removing damaged tissue in burn wounds.

Leukocidin

A bacterial toxin, most often produced by Staphylococcus aureus and some Streptococcus species, that specifically targets and destroys white blood cells (leukocytes). It works by forming pores in the cell membranes of these immune cells, causing them to rupture and die, which weakens the host’s defenses against infection. A well‑known example is Panton‑Valentine leukocidin (PVL), associated with severe skin infections and certain cases of necrotizing pneumonia.

α-toxin

A pore‑forming exotoxin produced by Staphylococcus aureus that damages host cell membranes. It binds to susceptible cells, assembles into heptameric pores, and causes leakage of ions and molecules, leading to cell lysis and tissue injury. This toxin contributes to the bacterium’s virulence by destroying red blood cells, immune cells, and other host tissues, playing a major role in infections such as pneumonia, sepsis, and skin abscesses.

Exfoliatin

A bacterial exotoxin produced by certain strains of Staphylococcus aureus that causes the skin’s outer layers to separate. It works by cleaving desmoglein‑1, a protein that helps hold skin cells together in the epidermis, leading to blistering and peeling. This toxin is responsible for conditions such as staphylococcal scalded skin syndrome (SSSS) and bullous impetigo, where widespread skin damage occurs due to the loss of cell adhesion.

Staphylococcal scalded skin syndrome

A severe skin condition caused by exotoxins (exfoliatins) released by certain strains of Staphylococcus aureus. These toxins break down proteins that hold skin cells together, leading to widespread blistering and peeling that resembles a burn or scald. SSSS primarily affects infants and young children, though it can occur in adults with weakened immunity, and it can progress rapidly if untreated.

Povidone-iodine

A broad‑spectrum antiseptic solution made by combining iodine with the polymer povidone, which helps release iodine slowly and reduce irritation. It is widely used to disinfect skin before surgery, clean wounds, and sterilize medical equipment because it is effective against bacteria, viruses, fungi, and protozoa. Unlike pure iodine, povidone‑iodine is less toxic and less irritating, making it safer for repeated medical and household use.

Toxic shock syndrome toxin

A superantigen exotoxin produced by certain strains of Staphylococcus aureus. It overstimulates the immune system by non‑specifically activating large numbers of T cells, leading to massive release of cytokines. This immune overreaction causes the symptoms of toxic shock syndrome, including fever, rash, low blood pressure, and multi‑organ involvement. TSST‑1 is considered a major virulence factor, enabling S. aureus to trigger severe systemic illness even when bacterial numbers are relatively low.

Toxic shock syndrome

A rare but life‑threatening condition caused by toxins released from Staphylococcus aureus or Streptococcus pyogenes. These toxins act as superantigens, overstimulating the immune system and triggering a massive release of cytokines. The result is sudden high fever, rash, low blood pressure, multi‑organ involvement, and in severe cases, shock. TSS is often linked to tampon use, surgical wounds, or skin infections, and requires urgent medical treatment to prevent rapid progression.

Superantigen

A type of microbial protein, usually produced by bacteria or viruses, that causes massive, non‑specific activation of T cells in the immune system. Unlike normal antigens, which activate only specific T cells through precise recognition, superantigens bind directly to the MHC class II molecules on antigen‑presenting cells and the T‑cell receptor outside the usual binding site. This bypass leads to activation of up to 20–30% of all T cells at once, triggering an overwhelming release of cytokines. The result is a dangerous immune overreaction that can cause fever, rash, shock, and multi‑organ damage, as seen in conditions like toxic shock syndrome.

Enterotoxin

A type of exotoxin that specifically targets the intestinal lining, disrupting normal cellular processes and causing symptoms like diarrhea, vomiting, and abdominal cramps. Produced by bacteria such as Escherichia coli, Vibrio cholerae, and Staphylococcus aureus, enterotoxins often work by altering ion transport or triggering excessive fluid secretion, leading to rapid dehydration and electrolyte imbalance. They are typically heat-labile or heat-stable, depending on the organism, and play a central role in foodborne illnesses and waterborne diseases. In microbiology, enterotoxins are studied for their mechanisms of action and their impact on public health and infection control.

Impetigo

A highly contagious superficial skin infection, most often caused by Staphylococcus aureus or Streptococcus pyogenes. It typically appears as red sores or blisters that rupture, ooze, and form a honey‑colored crust, most commonly on the face, arms, or legs. Impetigo spreads easily through direct contact or shared items and is especially common in children, though it can affect people of any age.

Streptococcus pyogenes

A Gram-positive, spherical bacterium that typically forms chains and belongs to Group A Streptococci (GAS). It is beta-hemolytic on blood agar, meaning it completely lyses red blood cells, and is catalase-negative and non-motile. This pathogen is responsible for a wide range of human diseases, from mild infections like strep throat and impetigo to severe conditions such as necrotizing fasciitis and streptococcal toxic shock syndrome. Transmission occurs through respiratory droplets or direct contact with infected wounds, and untreated infections can lead to serious complications like rheumatic fever or glomerulonephritis. Early diagnosis and antibiotic treatment are essential to prevent long-term sequelae.

Acne vulgaris

A common chronic skin condition that occurs when hair follicles become clogged with oil (sebum), dead skin cells, and sometimes bacteria. It typically presents as pimples, blackheads, whiteheads, and in more severe cases, nodules or cysts, most often on the face, chest, and back. The condition is influenced by factors such as hormonal changes, excess sebum production, and inflammation, and while not dangerous, it can cause scarring and emotional distress if untreated.

Cutibacterium acnes

(Formerly known as Propionibacterium acnes) a Gram‑positive, anaerobic bacterium that normally lives on human skin, especially in hair follicles and sebaceous glands. Formerly known as Propionibacterium acnes, it was reclassified in 2016 to better reflect its genetic relationships. While usually harmless as part of the normal skin flora, it plays a central role in acne vulgaris by contributing to inflammation when follicles become clogged with oil and dead skin cells. It can also act as an opportunistic pathogen, occasionally causing infections in prosthetic devices, eye surgery, or other invasive medical contexts.

Benzoyl peroxide

An organic compound widely used in dermatology and microbiology for its strong oxidizing and antimicrobial properties. Chemically, it consists of two benzoyl groups linked by a peroxide bond, which decomposes to release free radicals that disrupt microbial cell membranes and proteins. In acne treatment, it targets Cutibacterium acnes by introducing oxygen into anaerobic environments and promoting skin exfoliation (keratolysis). Concentrations in topical formulations typically range from 2.5% to 10%, and it is often combined with antibiotics for enhanced efficacy. Industrially, benzoyl peroxide also serves as a polymerization initiator and bleaching agent, though its reactive nature requires careful handling due to potential skin irritation and explosive risk in dry form.

Lyme disease

A bacterial infection caused by Borrelia burgdorferi, transmitted to humans through the bite of infected blacklegged ticks, especially in wooded or grassy areas. Early symptoms include fever, fatigue, headache, and a distinctive bull’s-eye rash called erythema migrans. If untreated, the bacteria can spread to the joints, heart, and nervous system, leading to complications like arthritis or neurological issues. Diagnosis involves clinical evaluation and blood tests, and treatment typically includes antibiotics such as doxycycline. Lyme disease highlights the intersection of microbiology, ecology, and public health, especially in regions with high tick populations.

Borrelia burgdorferi

A Gram‑negative, spiral‑shaped bacterium that causes Lyme disease, the most common tick‑borne illness in North America and Europe. It is transmitted to humans through the bite of infected blacklegged ticks (Ixodes species). Once inside the body, the bacterium can spread through the bloodstream to joints, the heart, and the nervous system, leading to symptoms such as rash (erythema migrans), fever, fatigue, and in later stages, arthritis or neurological complications.

Reservoir

(Microbiology) any natural habitat—living or non-living—where a pathogen normally lives, grows, and multiplies, serving as a long-term source of infection. Reservoirs can be humans, animals, or environmental sources like soil, water, or surfaces, and they may carry the pathogen symptomatically or asymptomatically. For example, humans are reservoirs for measles, while rodents can be reservoirs for hantavirus. The reservoir sustains the pathogen’s presence in nature, enabling transmission to susceptible hosts and shaping the ecology of infectious disease.

Vector

A living organism that transmits a pathogen from one host to another. Most commonly, vectors are arthropods such as mosquitoes, ticks, or fleas, which can carry viruses, bacteria, or parasites without necessarily being affected themselves. They act as biological bridges, enabling diseases like malaria, Lyme disease, or plague to spread between populations.

First stage of Lyme disease

Develops days to weeks after a tick bite and is characterized by the hallmark erythema migrans rash, which expands outward in a bull’s‑eye pattern. Patients often experience flu‑like symptoms such as fever, chills, fatigue, headache, and muscle or joint aches, reflecting the body’s initial immune response. At this stage, the infection is still near the site of entry, and prompt antibiotic treatment is highly effective in preventing progression to later, more serious stages involving the joints, heart, or nervous system.

Second stage of Lyme disease

Occurs weeks to months after the initial tick bite when Borrelia burgdorferi spreads through the bloodstream. Symptoms may include multiple erythema migrans rashes at different sites, neurological problems such as facial nerve palsy or meningitis, and cardiac issues like irregular heartbeat. At this stage, the infection is no longer localized and can affect multiple organ systems, making timely antibiotic treatment crucial to prevent progression to the chronic, late stage.

Third stage of Lyme disease

Develops months to years after the initial infection if untreated. At this stage, the bacteria can cause persistent arthritis, especially in the knees, along with neurological problems such as memory issues, numbness, or difficulty concentrating. Some patients may also experience chronic fatigue and heart rhythm disturbances, reflecting the widespread and long‑term impact of Borrelia burgdorferi on multiple organ systems.

Arthritis

A broad medical term that refers to inflammation of one or more joints, leading to symptoms such as pain, stiffness, swelling, and reduced mobility. It is not a single disease but a category that includes many types, the most common being osteoarthritis (caused by cartilage wear and tear) and rheumatoid arthritis (an autoimmune condition where the immune system attacks joint linings). Over time, arthritis can damage joints and affect daily function, making early recognition and management important for preserving mobility and quality of life.

Neurological change

Any alteration in the normal function of the nervous system, which may affect the brain, spinal cord, or peripheral nerves. These changes can manifest as new or worsening symptoms such as confusion, memory loss, weakness, numbness, vision problems, speech difficulties, or coordination issues. In medicine, recognizing neurological change is important because it may signal conditions like stroke, infection, trauma, or degenerative disease that require prompt evaluation.

Varicella

(Also commonly known as chickenpox) a highly contagious viral infection caused by the varicella‑zoster virus (VZV). It typically presents with an itchy, blister‑like rash that progresses from red spots to fluid‑filled vesicles and then scabs, often accompanied by fever, fatigue, and loss of appetite. While usually mild in children, varicella can be more severe in adults or immunocompromised individuals, and once resolved, the virus remains dormant in nerve tissue, with the potential to reactivate later in life as shingles.

Varicella-zoster virus

A double-stranded DNA virus from the Herpesviridae family that causes chickenpox (varicella) during primary infection and shingles (herpes zoster) upon reactivation. After initial infection—usually in childhood—VZV becomes latent in sensory nerve ganglia, where it can remain dormant for decades. Reactivation, often triggered by aging or immunosuppression, leads to shingles, a painful, localized skin rash. VZV spreads through respiratory droplets or direct contact with lesions and is highly contagious during the chickenpox phase. Vaccines are available for both chickenpox and shingles, making VZV a key example of a latent viral infection with significant public health relevance.

Lesion

A general medical term for any abnormal change or damage in tissue, whether caused by injury, infection, disease, or other processes. Lesions can occur in skin, organs, or bones and may appear as spots, sores, growths, or structural disruptions. The term is broad and descriptive, often used by clinicians until the specific nature or cause of the abnormality is identified.

Latent

Refers to a stage in an infection where the pathogen is present in the host but remains inactive or dormant, causing no noticeable symptoms. During latency, the microorganism may persist silently for weeks, months, or even years, and can reactivate later under certain conditions, such as immune suppression. Examples include herpes simplex virus, tuberculosis, and HIV. In microbiology, latency highlights the challenge of detecting and managing infections that hide within the host without immediate signs.

Herpes zoster

(Also commonly known as shingles) a painful skin rash caused by the reactivation of varicella-zoster virus (VZV), the same virus that causes chickenpox. After a person recovers from chickenpox, VZV remains latent in sensory nerve ganglia and can reactivate years later, typically due to aging, stress, or immunosuppression. The rash usually appears as a band or strip of blisters on one side of the body or face, often accompanied by burning pain, tingling, or itching. Herpes zoster is more common in older adults and can lead to complications like postherpetic neuralgia, a persistent nerve pain after the rash resolves. Vaccination can reduce the risk and severity of shingles.

Acyclovir

An antiviral drug commonly used to treat infections caused by herpes viruses, such as herpes simplex (cold sores and genital herpes), varicella‑zoster (chickenpox and shingles), and sometimes Epstein‑Barr virus. It works by mimicking a natural nucleoside and interfering with viral DNA synthesis, which stops the virus from multiplying inside human cells. Acyclovir can be taken orally, applied as a topical cream, or given intravenously depending on the severity of infection. Because it targets viral replication without harming normal cells, it is widely prescribed and considered safe for long‑term use in managing recurrent herpes infections.

Measles, mumps, and rubella vaccine (MMRV)

A combined attenuated whole agent vaccine that contains live but weakened forms of the measles, mumps, and rubella viruses. It is designed to mimic natural infection without causing disease, stimulating a strong and long‑lasting immune response that protects against all three illnesses. The MMR vaccine is typically given in childhood in two doses and has been highly effective in reducing the incidence of these once‑common viral diseases worldwide.

Measles

A highly contagious viral infection caused by the measles virus (a paramyxovirus), primarily affecting the respiratory system and immune cells. It spreads through airborne droplets from coughing or sneezing and typically begins with fever, cough, runny nose, and conjunctivitis, followed by a distinctive red rash that starts on the face and spreads downward. A hallmark sign is Koplik spots—tiny white lesions inside the cheeks. Mea can lead to serious complications like pneumonia, encephalitis, and immune suppression, especially in young children and immunocompromised individuals. Vaccination with the MMR (measles, mumps, rubella) vaccine is the most effective prevention.

Measles virus

A highly contagious pathogen belonging to the Paramyxoviridae family, genus Morbillivirus. It is an enveloped, single‑stranded RNA virus that spreads through respiratory droplets and infects the respiratory tract and immune cells. The virus causes measles (rubeola), an illness marked by fever, cough, runny nose, conjunctivitis, and a characteristic red rash. Because of its ability to suppress the immune system and lead to complications such as pneumonia or encephalitis, measles virus is considered one of the most serious childhood pathogens, though it is preventable through vaccination with the MMR vaccine.

Koplik spot

A small, bluish‑white or gray lesion with a reddish halo that appears on the inner lining of the cheek, most often opposite the upper molars. It resembles a grain of salt on a red background and is considered pathognomonic for measles, meaning it is a distinctive diagnostic sign of the disease. Koplik spots usually emerge 1–4 days before the measles rash, serving as an important early clinical clue for physicians to recognize and confirm infection.

Macular rash

A skin eruption made up of flat, discolored spots called macules that do not rise above the surface of the skin. Each macule is usually less than 1 cm in diameter, smooth to the touch, and can appear in different colors depending on the underlying cause and the person’s skin tone. Unlike papular rashes, which involve raised bumps, macular rashes remain level with the surrounding skin. They often occur in conditions such as viral infections (measles, rubella), drug reactions, or systemic illnesses, making them an important diagnostic clue in clinical practice.

Viral pneumonia

A lung infection caused by viruses such as influenza, respiratory syncytial virus (RSV), adenovirus, or coronaviruses, leading to inflammation and fluid buildup in the alveoli that makes breathing difficult. It often presents with fever, cough, chest pain, fatigue, and shortness of breath, and can range from mild illness to severe, life‑threatening disease, especially in children, older adults, or those with weakened immune systems. Unlike bacterial pneumonia, antibiotics are ineffective, so treatment focuses on supportive care and, in some cases, antiviral medications. Vaccination against viruses like influenza, measles, and COVID‑19 helps reduce the risk of developing viral pneumonia.

Encephalitis

An inflammation of the brain tissue, most often caused by viral infections such as herpes simplex virus, arboviruses, or enteroviruses, though bacteria, parasites, or autoimmune reactions can also be triggers. The swelling interferes with normal brain function and may lead to symptoms like fever, headache, confusion, seizures, or changes in behavior and consciousness. Severity ranges from mild illness to life‑threatening disease, and prompt medical evaluation is critical because encephalitis can cause lasting neurological damage if untreated.

Subacute sclerosing panencephalitis

A rare, progressive, and often fatal neurological disorder caused by a persistent, mutated measles virus that remains in the brain after an initial infection, typically occurring in children or adolescents several years post-measles. The virus triggers chronic inflammation, demyelination, and degeneration of brain tissue, leading to symptoms such as personality changes, cognitive decline, motor dysfunction, seizures, and eventually coma and death. SSPE reflects a delayed viral complication and underscores the critical importance of measles vaccination in preventing long-term, devastating outcomes.

Rubella

(Also commonly known as German measles) a contagious viral illness caused by the rubella virus in the Togaviridae family. It typically produces a mild fever, swollen lymph nodes, and a fine pink rash that spreads from the face downward. While rubella is usually mild in children and adults, it is especially dangerous during pregnancy because it can lead to congenital rubella syndrome, causing birth defects such as deafness, heart problems, or developmental delays. The disease is preventable through the MMR vaccine, which provides protection against measles, mumps, and rubella.

Rubella virus

The pathogen that causes rubella (German measles), belonging to the Togaviridae family, genus Rubivirus. It is an enveloped, single‑stranded RNA virus that spreads mainly through respiratory droplets and infects the respiratory tract. The virus typically produces a mild illness with fever, swollen lymph nodes, and a fine pink rash, but it is especially dangerous in pregnancy because it can cross the placenta and cause congenital rubella syndrome, leading to birth defects such as deafness, heart problems, or developmental delays. Prevention is achieved through the MMR vaccine, which protects against measles, mumps, and rubella.

Congenital rubella syndrome

A group of birth defects that occur when a fetus is infected with the rubella virus during pregnancy, especially in the first trimester. The virus crosses the placenta and disrupts normal development, leading to problems such as deafness, heart defects, cataracts, developmental delays, and growth restriction. CRS can also cause liver and spleen enlargement, bone abnormalities, and in severe cases, miscarriage or stillbirth. Because rubella infection in pregnancy is the sole cause, prevention relies on MMR vaccination before pregnancy, which has made CRS rare in countries with strong immunization programs.

Wart

A small, rough growth on the skin caused by infection with certain strains of the human papillomavirus (HPV). Warts are noncancerous and can appear on different parts of the body, most commonly the hands, feet, and face. They spread through direct contact with the virus, often via breaks in the skin, and may resolve on their own over time, though treatments like cryotherapy, salicylic acid, or laser removal can help.

Human papillomavirus (HPV)

A group of viruses that infect the skin and mucous membranes, often spread through direct skin‑to‑skin or sexual contact. Some types cause harmless growths like warts, while others are linked to cancers such as cervical, anal, or throat cancer. Most infections clear on their own, but certain high‑risk strains can persist and lead to serious disease. Vaccines are available that protect against the most dangerous types, making HPV prevention an important part of public health.

Liquid nitrogen

Nitrogen cooled into a liquid state at about −196 °C (−321 °F), making it extremely cold and useful as a cryogenic fluid. It is colorless, odorless, and non‑flammable, produced by fractional distillation of liquid air. Because of its low temperature, it is widely used in medicine (cryosurgery, tissue preservation), food processing (instant freezing), and industry (cooling, shrink‑fitting metals). While chemically inert, direct contact can cause severe frostbite, so it must be handled with care.

Salicylic acid

An organic compound found naturally in plants like willow bark and wintergreen, and it is widely used in medicine and skincare. Chemically known as 2‑hydroxybenzoic acid, it works by breaking down the bonds between dead skin cells, making it an effective exfoliant for treating acne, dandruff, psoriasis, and warts. It also serves as the precursor to aspirin (acetylsalicylic acid), one of the most common pain‑relieving drugs. While generally safe in controlled amounts, excessive use can irritate the skin, so concentrations are carefully regulated in topical products.

Cutaneous mycoses

Superficial fungal infections of the skin, hair, and nails caused mainly by dermatophytes such as Trichophyton, Microsporum, and Epidermophyton. These fungi digest keratin, the protein that strengthens these tissues, which is why they specifically target them. Common examples include athlete’s foot (tinea pedis), ringworm (tinea corporis), jock itch (tinea cruris), and nail fungus (tinea unguium). Symptoms often involve itching, scaling, redness, or brittle nails, and the infections spread through direct contact with infected people, animals, or contaminated surfaces, but they usually remain limited to the outer layers of the body without invading deeper tissues.

Ringworm

A common fungal infection of the skin caused by dermatophytes, not by worms despite its name. It appears as a red, circular, scaly rash with clearer skin in the center, giving it a ring‑like shape. Ringworm can affect different body areas, such as the scalp (tinea capitis), body (tinea corporis), feet (tinea pedis, or athlete’s foot), and groin (tinea cruris, or jock itch). It spreads through direct contact with infected people, animals, or contaminated surfaces, and while uncomfortable, it usually remains superficial and is treatable with antifungal medications.

Athlete’s foot

A common fungal infection of the skin, usually affecting the spaces between the toes. It is caused by dermatophyte fungi that thrive in warm, moist environments such as sweaty shoes, locker rooms, and public showers. Symptoms include itching, burning, scaling, and cracked skin, sometimes with blisters. Although uncomfortable, the infection remains superficial and is treatable with antifungal creams, sprays, or powders, along with good foot hygiene to prevent recurrence.

Jock itch

A common fungal infection of the groin area, medically called tinea cruris. It is caused by dermatophyte fungi that thrive in warm, moist environments, making the inner thighs, buttocks, and genital region especially vulnerable. Symptoms include itching, redness, a ring‑shaped rash, and flaking or cracking skin, often with well‑defined edges. The infection spreads through direct contact or contaminated clothing and towels, and while uncomfortable, it remains superficial and is treatable with antifungal creams, powders, and good hygiene practices.

Azole

A type of antifungal drug that works by blocking the synthesis of ergosterol, an essential component of fungal cell membranes. Without ergosterol, the membrane becomes unstable, leading to inhibited growth or death of the fungus. Azoles are widely used to treat infections ranging from superficial conditions like athlete’s foot and yeast infections to serious systemic fungal diseases. They are divided into two main groups: imidazoles (e.g., ketoconazole, clotrimazole) and triazoles (e.g., fluconazole, itraconazole, voriconazole), which differ slightly in structure and clinical use.

Griseofulvin

An antifungal drug that works by interfering with fungal cell division. It binds to microtubules and disrupts the mitotic spindle, preventing the fungus from properly replicating its DNA during cell division. Griseofulvin is taken orally and becomes concentrated in keratin-rich tissues like skin, hair, and nails, making it especially useful for treating dermatophyte infections such as ringworm, athlete’s foot, and nail fungus. Because it acts slowly and requires long treatment courses, it is generally reserved for persistent or widespread infections.

Candidiasis

An infection caused by Candida species, most often Candida albicans, a type of yeast that normally lives harmlessly on the skin, in the mouth, gut, and genital tract. When conditions allow the yeast to overgrow—such as weakened immunity, antibiotic use, or excess moisture—it can cause disease. Forms include oral thrush (white patches in the mouth), vaginal yeast infection (itching, discharge), and skin infections in moist areas. In severe cases, Candida can enter the bloodstream and cause systemic infection, which is dangerous and requires urgent treatment. While usually mild and treatable with antifungal medications, candidiasis highlights how a normal resident organism can become pathogenic under the right circumstances.

Candida albicans

A species of yeast that normally lives on human skin, in the mouth, gut, and genital tract as part of the normal microbiota. It is usually harmless, but under certain conditions—such as weakened immunity, antibiotic use, or excess moisture—it can overgrow and cause infection known as candidiasis. This organism is notable for being dimorphic, meaning it can switch between yeast and filamentous forms, which helps it invade tissues. While most infections are mild (like oral thrush or vaginal yeast infections), C. albicans can cause serious systemic disease if it enters the bloodstream.

Yeast infection

A common condition caused by the overgrowth of Candida yeast, most often Candida albicans, in areas such as the mouth, skin, or genital tract. It produces symptoms like itching, irritation, discharge, or white patches, depending on the site of infection. While usually mild and treatable with antifungal medications, yeast infections can recur and, in rare cases, become serious if the yeast spreads deeper into the body.

Thrush

A fungal infection in the mouth and throat caused by the overgrowth of Candida yeast, most often Candida albicans. It appears as white, creamy patches on the tongue, inner cheeks, or throat, which may cause soreness, redness, or difficulty swallowing. Thrush is more common in infants, people using antibiotics or inhaled steroids, and those with weakened immune systems, but it is usually mild and treatable with antifungal medication.

Vaginitis

An inflammation of the vagina that can cause symptoms such as itching, irritation, abnormal discharge, and discomfort during urination or sex. It has several possible causes, including infections (like yeast, bacterial vaginosis, or trichomoniasis), hormonal changes (such as low estrogen after menopause), or irritation from chemicals and poor hygiene. While often mild and treatable, identifying the specific cause is important because treatment depends on whether the vaginitis is due to fungi, bacteria, parasites, or non‑infectious factors.

Nystatin

An antifungal medication derived from Streptomyces noursei that is used to treat infections caused by Candida yeast, such as oral thrush, skin infections, and intestinal candidiasis. It belongs to the polyene class of antifungals and works by binding to ergosterol in fungal cell membranes, creating pores that cause the cells to leak and die. Because it is not absorbed into the bloodstream when taken orally, nystatin is mainly effective for local infections rather than systemic disease. It is available in forms like oral suspension, tablets, creams, and ointments, and is generally safe, though mild side effects such as nausea or skin irritation can occur.