Lecture Notes on Waxes and Humectants
Waxes
Definition: Natural waxes are natural esters consisting of a fatty acid attached to a long-chain fatty alcohol.
- The alcohol component has a hydroxyl group (alcohol functional group).
- Long hydrocarbon chains, generally 16-30 carbon atoms in length.
- Joined by an ester linkage via dehydration synthesis.
- Lack a glycerol backbone, unlike triglycerides.
- Essentially fatty acids and fatty alcohols joined.
Properties:
Often saturated and have long chains, making them harder, less greasy, and more brittle.
Typically solid at room temperature.
Melting points generally above 45°C.
Exception:
Jojoba oil is a liquid wax.
Melting Points:
Different waxes have different melting points.
Lipstick formulation example: Waxes must be solid in the stick but melt upon skin contact.
Microbial Resistance:
Waxes are resistant to microbial attack; microbes generally don't use them as a food source.
Preservatives:
Solid waxy formulas (e.g., lip balms) may not require preservatives.
Considerations:
Resistant to moisture and oxidation.
Can alter product thickness and melting point.
May add heaviness, requiring adjustments to the formula.
Sources:
- Animal Waxes:
- Beeswax (solid at room temperature).
- Lanolin (from sheep's wool).
- Historically used as a moisturizer but can be comedogenic and contain contaminants.
- Modern lanolin is often chemically modified and purified to remove undesirable qualities.
- Plant Waxes:
- Produced by plants to prevent water evaporation.
- Examples: carnauba, candelilla, jojoba.
- Often come in flake form.
- Used in color cosmetics.
- Modifications:
- PEG modifications (adding hydroxyl groups).
- Examples: PEG oils, PEG waxes, PEG six, PEG eight beeswax, peg six, peg 20 sorbitum beeswax, silicone and beeswax.
- Mineral Waxes:
- From soils and petroleum byproducts.
- Examples: ozokerite, paraffin, microcrystalline, ceresin.
- Synthetic Waxes:
- Paraffin wax is a basic synthetic wax.
- Polyethylene and carbo waxes.
- Paraffin wax is often used in candles.
- Can add brittleness to products.
Humectants
Definition: Polar substances that absorb water vapor and draw water to themselves.
Function:
- Part of the water phase of an emulsion.
- Hygroscopic/hydrophilic: attract and hold onto water via hydrogen bonds.
- Typical concentration: 1-5% in a formula (can be higher in serums).
Benefits in Emulsions:
- Hydrating Effect: Retain water to reduce transepidermal water loss (TEWL).
- Prevent Product Dehydration: Maintain product hydration over its lifespan.
- Reduce Free Water:
- Humectants bind water molecules, reducing free water.
- Free water is the first to evaporate and can be used by microbes for replication.
Mechanism: Ability to form hydrogen bonds due to hydroxyl groups (-OH) or oxygen atoms.
Examples:
- Glycerin:
- Benchmark humectant.
- Has a hydrocarbon backbone with a hydroxyl group attached to each carbon.
- Can modify aquaporin channels in the epidermis to enhance water delivery, and is considered a cosmeceutical.
- May feel tacky at concentrations above 5%.
- Sorbitol:
- Similar to glycerin, with hydroxyl groups on each carbon.
- Common in toothpaste due to its humectancy and slight sweetness.
- Hyaluronic Acid:
- Large molecule with hydrocarbon structures and numerous oxygen-containing functional groups.
- Binds times its weight in water.
Sources of Water:
- Water within the formulation.
- Water from the viable epidermal and dermal layers.
- Water from the surrounding air (in high humidity).
Water Binding and TEWL:
- Humectants pull water from within the skin to the stratum corneum, preventing TEWL.
- May increase TEWL if not combined with occlusive ingredients (e.g., ceramides, dimethicone, silicas).
Aquaporins/Aquaglyceroporins:
- Protein channels in keratinocyte plasma membranes that transport water and glycerin.
- Present from the basal layer to the granular layer.
- Non-functional in stratum corneum to prevent rapid water loss.
Environmental Factors:
- High humidity (>70%) allows skin to absorb water from the air.
- Steam facials provide a high-humidity environment to hydrate skin.
- Moisturizing creams are crucial after facials to prevent water loss.
Common Humectant Ingredients:
Glycerin, sorbitol, urea.
Components of natural moisturizing factors (NMF) in the stratum corneum.
Examples: pyrrolidone carboxylic acid (PCA), sodium lactate, alpha hydroxy acids (AHAs), lactic acid, urea.
Alternatives to glycerin: hexylene glycol, butylene glycol, propylene glycol, MP diol.
Glycerin Detailed:
Still one of the most commonly used humectants in products.
Measure for how humid something is.
Has a reservoir effect in the skin.
Exhibiting action on the skin that makes it a cosmeceutical.
Can modify aquaporin channels within the epidermis to enhance the delivery of water.
Sorbitol Detailed:
Longer hydrocarbon chain than glycerin, with hydroxyl groups.
Usually in powder form or a 70% aqueous solution.
Hexylene, Butylene, and Propylene Glycol Detailed:
Common in facial emulsions.
Do not have the sticky after-feel of glycerin.
Used in foundations to help spread pigment without streaking.
Also can be used as a penetration enhancer, but with limitations on its use because of its ability to potentially enhance the delivery of less desirable things.
MPDIOL:
Similar, but cheaper in formulas.
Natural Moisturizing Factor (NMF) Ingredients:
Hydroxyl groups or oxygen creates polar qualities.
Alpha Hydroxy Acids (AHAs):
Also known as peeling agent; used for skin peels, chemical skin peels.
AHAs + urea both have a crashlytic and desmolytic effect, but can also both have humectant qualities to them.
$<10$%
- humectant with 0.1% 3% concentration
$>10$%
- caratolitic or desmolitic properties
Hyaluronic Acid (HA):
High molecular weight polymer that is made from subunits.
Huge water-binding capacity due to polar areas.
High Molecular Weight ( > 500,000 Daltons):
- Forms a moisturizing viscoelastic film on the skin surface and is an occluded