Dermatological Drugs I

Introduction by Dr. Jan on dermatological drugs
Focus of the lecture: sunscreen, a product that protects our skin from harmful effects of sunlight.
- Sunlight can cause skin damage, including sunburn and even skin cancer over time.
Personal experience in developing sunscreens, suggesting practical knowledge in how they work.
Goal: enhance understanding of skin and sunscreen, emphasizing why protection is essential.

Overview of skin structure:

  - Epidermis: This is the outermost layer of the skin. It acts as a barrier to protect the body from the environment, including dirt and pathogens.

  - Dermis: Located beneath the epidermis, this layer contains connective tissue, hair follicles, and sweat glands, playing a crucial role in skin strength and elasticity.

  - Hypodermis (subcutaneous layer): The deepest layer of skin, which consists mainly of fat. This layer provides insulation, energy storage, and helps to absorb shocks from impacts.
Key point: Only the bottom-most layer of the epidermis is actively dividing; the cells above it are dead or dying, meaning they no longer function to rebuild the skin but serve as protection.
Protection Focus: It is essential to protect the living cells in the bottom of the epidermis and the dermis to maintain healthy skin.
Light Penetration: UV light does not reach the deepest layers; it mainly affects the upper layers of skin, meaning only the outermost parts are primarily at risk when we are exposed to sunlight.

DNA Absorption:
- UV light can be absorbed by the DNA found in our cells, especially at specific parts called thymine nucleotides.
- When this happens, molecules known as thymine dimers form, which are effectively two thymine bases that bond incorrectly instead of being properly separated.
Consequences of Thymine Dimers:
- The formation of these dimers prevents the accurate replication of DNA. If DNA cannot replicate properly, this can lead to issues like cell death or the development of cancer, as damaged DNA can instruct cells to grow uncontrollably.

Types of Light:
  - Infrared: While generally associated with heat, infrared light is not a primary concern when discussing skin protection.
  - Visible Light: This is the light that we can see, but it poses less risk to our skin compared to UV light.
  - UV Light: Although we can't see it, UV light is particularly damaging and an important concern for skin health.
Graph Analysis:
  - X-axis: Wavelength of light, which affects the light's energy.
  - Y-axis: Irradiance, or the intensity of light.
  - Relationship: A lower wavelength means higher energy; this is important because UV light, having a shorter wavelength, is far more powerful than visible light.

UV Spectrum: UV light is divided into three main types:
  - UVC: This type has the highest energy but is mostly absorbed by the ozone layer, so it is not typically a concern for humans.
  - UVB: This is the second highest energy type and is mainly responsible for causing sunburn.
  - UVA: While having lower energy, UVA rays can penetrate the skin deeply, leading to DNA damage and contributing to premature aging of the skin as well as tanning.
Key Concept:
- UVB causes erythemal damage, which we commonly recognize as sunburn, indicating clear skin injury.
- UVA rays are more insidious, causing DNA damage that can result in long-term health issues while also being the reason for tanning, which is a protective response of the skin.

Discussion on tanning beds which primarily emit UVA rays.
Calling tanning beds "death beds" highlights the serious risks associated with using these beds, especially the likelihood of DNA damage that can lead to skin diseases or cancer due to overexposure to UVA rays.

SPF (Sun Protection Factor):
- Definition: A numerical value that gives an estimate of how long you can stay in the sun without burning when using sunscreen compared to not using it.
- SPF Calculation: The calculation compares the time to burn with sunscreen versus without it. For example, if you burn in 10 minutes without sunscreen, SPF 2 would mean you could theoretically last 20 minutes before burning.
Testing Methodology:
- Measured on real skin by exposing it to UV light while applying 2 mg/cm² of sunscreen. It’s crucial to apply enough for it to be effective.
- Using less than this amount can significantly reduce the sunscreen's overall protection quality, putting skin at risk.
UVB Focus: Most SPF measurements focus primarily on protecting against UVB rays, which are mainly responsible for sunburn.
UVA Protection: Look for labels that indicate broad-spectrum protection, which includes both UVA and UVB protection, although there isn't a numerical measure yet for UVA effectiveness.
Water Resistance:
- It’s also vital to consider how different conditions affect sunscreen effectiveness, like water exposure; typical sunscreen labels might indicate they are water-resistant for either 40 or 80 minutes.

Two Main Categories:
- Organic Filters: These are chemical compounds that either absorb or reflect UV light, subdivided into UVA filters and UVB filters.
- Inorganic Filters: They contain minerals like titanium dioxide or zinc oxide, which provide broad absorption for both UVA and UVB rays and are gentler on the skin.
Historical Context:
- Early sunscreens primarily focused on UVB protection using para-aminobenzoic acid (PABA), but its use has declined due to allergic reactions and negative effects on clothing.
- PABA was replaced by octanoxate, but this too is reducing in popularity due to its potential for irritation.
Common UVB Filters:
- Other than octanoxate, common UVB filters include homosalate, octosalate, and octacrylene, which help to absorb UVB rays effectively.
UVA Filters:
- Prominent UVA filters include oxybenzone and avobenzone. Avobenzone is noted for its effectiveness but has stability issues, breaking down when exposed to UV light.
- To help with this, octocrylene is often used alongside avobenzone to improve its stability, but they can sometimes be incompatible in certain sunscreen formulas.

Historically, sunscreens appeared white due to the use of titanium dioxide and zinc oxide as inorganic filters.
Advances in sunscreen technology allow for the creation of nanoparticles, which can be used in formulations to make the sunscreen appear clear while still effectively blocking UV light, making them more appealing to users who prefer non-whitening products.