G–L

The science behind the ingredients in skincare.

G

Glycerin

Also known as: Glycerol
Type: Trihydric alcohol / humectant

A naturally occurring three-carbon alcohol found throughout biological systems and widely used in cosmetics.

In skincare: One of the most established humectants, helping attract and retain water within the outer layers of the skin.

Skin biology: Glycerol is naturally present in the stratum corneum and contributes to normal skin hydration.

Formulation note: Its concentration affects both hydration and sensory properties; very high levels can produce a sticky skin feel.

Glyceryl Stearate

Type: Fatty-acid ester / emulsifier

An ester of glycerin and stearic acid.

In skincare: Functions as an emollient, emulsifier, consistency agent, and skin-conditioning ingredient.

Formulation benefit: Helps provide creams and lotions with a smooth, structured texture.

Glyceryl Stearate SE

Type: Self-emulsifying fatty ester

A form of glyceryl stearate containing additional soap-forming components that allow it to contribute more strongly to emulsification.

In skincare: Used to help stabilize oil-in-water emulsions while also contributing emollience and texture.

Glycolic Acid

Type: Alpha hydroxy acid (AHA)

The smallest and one of the most widely studied alpha hydroxy acids.

In skincare: Used for chemical exfoliation, improved skin texture, radiance, and the appearance of uneven pigmentation and fine lines.

Skin biology: Its small molecular size allows it to interact efficiently with the stratum corneum, although penetration and activity depend strongly on formulation pH, concentration, and exposure.

Glycyrrhiza Glabra Root Extract

Common name: Licorice root extract
Type: Botanical extract

An extract derived from the roots of Glycyrrhiza glabra.

In skincare: Commonly used in formulations addressing uneven pigmentation, redness, and skin comfort.

Composition: Licorice contains multiple bioactive constituents, including glycyrrhizin and various flavonoid compounds.

Gluconolactone

Type: Polyhydroxy acid (PHA)

A cyclic ester that gradually hydrolyzes to gluconic acid.

In skincare: Provides gentle exfoliation and humectant activity and is often incorporated into formulations designed for sensitive skin.

Formulation note: PHAs generally have larger molecular structures than many AHAs, contributing to their characteristically milder exfoliating profile.

Glutathione

Type: Tripeptide antioxidant

A small peptide composed of glutamate, cysteine, and glycine.

In biology: Glutathione is one of the body's major intracellular antioxidant systems.

In skincare: Used in formulations positioned around antioxidant protection and skin-brightening/complexion-evening benefits.

Important distinction: Topical glutathione's behavior depends substantially on formulation stability, delivery, and molecular environment.

Glycine

Type: Amino acid

The smallest proteinogenic amino acid.

In skincare: Functions primarily as a skin-conditioning ingredient and may also appear as part of peptide, protein, or amino-acid-based systems.

Skin biology: Glycine is an important constituent of collagen's amino-acid sequence.

H

Hamamelis Virginiana Leaf Extract

Common name: Witch hazel
Type: Botanical extract

An extract obtained from Hamamelis virginiana.

In skincare: Traditionally used for astringent, skin-conditioning, and soothing formulations.

Formulation note: Witch-hazel preparations vary considerably depending on extraction method and whether they contain significant amounts of alcohol.

Helianthus Annuus Seed Oil

Common name: Sunflower seed oil
Type: Botanical lipid

A vegetable oil rich in fatty acids, particularly linoleic acid in many grades.

In skincare: Functions as an emollient and skin-conditioning lipid.

Skin biology: Linoleic acid is an essential fatty acid involved in epidermal lipid organization and barrier function.

Hemi-Squalane

Type: Lightweight emollient

A branched hydrocarbon used as a lightweight alternative to heavier oils.

In skincare: Provides silky slip, spreadability, and lightweight emollience.

Formulation benefit: Useful in formulations designed to provide a dry, elegant skin finish.

Hyaluronic Acid

Also known as: Hyaluronan / sodium hyaluronate depending on form
Type: Glycosaminoglycan / polysaccharide

A naturally occurring polysaccharide found in skin and other connective tissues.

In skincare: Primarily valued for its water-binding and film-forming properties.

Skin biology: Hyaluronan is an important component of the extracellular matrix and contributes to tissue hydration and mechanical properties.

Important distinction: "Hyaluronic acid" products may contain molecules of different molecular weights, and molecular size can influence their behavior within a formulation and on the skin.

Hydrolyzed Hyaluronic Acid

Type: Lower-molecular-weight hyaluronan preparation

Hyaluronic acid that has been broken down into smaller molecular fractions.

In skincare: Used primarily for hydration and skin conditioning.

Formulation note: "Hydrolyzed" does not specify one precise molecular weight; supplier specifications are important when evaluating the ingredient.

Hydrolyzed Collagen

Type: Protein hydrolysate

Collagen broken down into smaller peptide fragments.

In skincare: Primarily functions as a humectant, conditioning, and film-forming ingredient.

Important distinction: Topically applied hydrolyzed collagen does not simply penetrate the skin and become new dermal collagen.

Hydrolyzed Oat Protein

Type: Plant protein hydrolysate

Oat proteins enzymatically or chemically broken into smaller peptides.

In skincare: Used as a conditioning and moisturizing ingredient and can contribute to a soft skin feel.

I

Idebenone

Type: Quinone / antioxidant

A synthetic analogue related structurally to coenzyme Q10.

In skincare: Used primarily in formulations focused on antioxidant protection and visible signs of environmental aging.

Formulation note: Its stability and delivery characteristics depend on the vehicle and overall formulation.

Inositol

Also known as: Myo-inositol
Type: Cyclic polyol

A naturally occurring carbohydrate-like compound involved in cellular signaling.

In skincare: Used as a skin-conditioning ingredient and appears in some formulations designed to support healthy-looking skin.

Skin biology: Inositol-containing phospholipids participate in important cellular signaling pathways.

Isoamyl Laurate

Type: Emollient ester

An ester used to provide lightweight emollience.

In skincare: Contributes spreadability, softness, and a dry, elegant skin feel.

Formulation benefit: Particularly useful in lightweight creams, lotions, sunscreens, and serum-like emulsions.

Isopropyl Myristate

Type: Fatty ester / emollient

An ester derived from isopropyl alcohol and myristic acid.

In skincare: Used as an emollient, solvent, and spreading agent.

Formulation note: It can provide excellent slip but may not be appropriate for every formulation intended for blemish-prone skin.

Isostearyl Alcohol

Type: Branched fatty alcohol

A long-chain branched alcohol used in cosmetic formulations.

In skincare: Functions as an emollient and consistency modifier.

Important distinction: Like cetyl and stearyl alcohol, this is a fatty alcohol and is chemically and functionally different from volatile alcohols such as ethanol.

J

Jojoba Esters

Type: Wax esters

Esters derived from jojoba-derived fatty acids and fatty alcohols.

In skincare: Provide emollience, conditioning, and texture modification.

Skin biology: Their wax-ester chemistry gives them properties distinct from conventional triglyceride-rich vegetable oils.

Jojoba Seed Oil

INCI: Simmondsia Chinensis Seed Oil
Type: Botanical wax ester

Oil-like material obtained from the seeds of Simmondsia chinensis.

In skincare: Functions as an emollient and skin-conditioning ingredient.

Formulation science: Unlike most plant oils, jojoba is composed predominantly of wax esters rather than triglycerides, contributing to its distinctive stability and sensory characteristics.

K

Kaolin

Type: Mineral clay

A naturally occurring clay composed primarily of the mineral kaolinite.

In skincare: Used as an absorbent, cleansing, texturizing, and opacifying ingredient.

Formulation use: Common in masks and cleansing products where absorption of excess surface oil is desired.

Important distinction: Excessive or frequent use in certain skin types can contribute to dryness depending on the complete formulation.

Kojic Acid

Type: Fungal-derived organic compound

A compound produced by certain fungi during fermentation.

In skincare: Used primarily in products targeting uneven pigmentation and dark spots.

Skin biology: Its cosmetic activity is associated with interference with tyrosinase-dependent melanin synthesis.

Formulation note: Kojic acid can be susceptible to oxidation and discoloration, making formulation stability important.

Keratin

Type: Structural fibrous protein

A family of proteins forming major structural components of the epidermis, hair, and nails.

In skin: Keratins provide mechanical strength and structural integrity to keratinocytes.

Topical skincare: Hydrolyzed keratin is primarily used as a conditioning or film-forming ingredient and should not be confused with rebuilding the living epidermal keratin network.

L

Lactic Acid

Type: Alpha hydroxy acid / organic acid

An organic acid naturally produced during cellular metabolism and found in fermented foods and other biological systems.

In skincare: Functions as an exfoliant and humectant and is widely used to improve the appearance of texture, dullness, and uneven pigmentation.

Skin biology: Lactic acid belongs to the skin's natural moisturizing factor system and therefore has both exfoliating and hydration-related relevance.

Lactobionic Acid

Type: Polyhydroxy acid (PHA)

An oxidation product of lactose consisting of a sugar acid linked to galactose.

In skincare: Used for gentle exfoliation, hydration, and skin conditioning.

Formulation benefit: Its larger molecular structure generally produces slower penetration than smaller AHAs, making it attractive for sensitive-skin formulations.

Lanolin

Type: Natural wax / lipid

A complex mixture of esters, alcohols, fatty acids, and related compounds obtained from sheep's wool.

In skincare: Functions as an emollient, occlusive, and skin-conditioning ingredient.

Formulation science: Lanolin can provide substantial barrier-like conditioning and is particularly useful in rich creams and protective products.

Important consideration: Some individuals may be sensitive to components of lanolin or highly refined lanolin preparations.

L-Ascorbic Acid

Also known as: Pure vitamin C / ascorbic acid
Type: Water-soluble antioxidant

The principal biologically active form of vitamin C used in topical skincare.

In skincare: Supports antioxidant defense, collagen-related biological processes, and complexion-evening formulations.

Formulation challenge: It is highly sensitive to oxidation and requires careful control of pH, oxygen exposure, light, water activity, and packaging.

Lecithin

Type: Phospholipid mixture

A mixture of phospholipids and related lipids obtained from sources such as soy or sunflower.

In skincare: Functions as an emollient, emulsifier, skin-conditioning agent, and delivery-system component.

Skin biology: Phospholipids are fundamental components of biological membranes, making lecithin particularly relevant to biomimetic formulation strategies.

Licorice Root Extract

INCI: Glycyrrhiza Glabra Root Extract
Type: Botanical extract

An extract of licorice root containing a complex mixture of phytochemicals.

In skincare: Commonly used in formulations targeting uneven tone, visible redness, and skin comfort.

Key constituents: Depending on the extract, relevant compounds may include glycyrrhizin, glabridin, liquiritin, and other flavonoids.

Linoleic Acid

Type: Essential polyunsaturated fatty acid / omega-6 fatty acid

An essential fatty acid that humans must obtain through diet.

In skin: Plays an important role in epidermal lipid organization and barrier function.

In skincare: Used as an emollient and lipid ingredient, particularly in formulations designed around barrier-supportive lipid systems.

Limonene

Type: Monoterpene

A naturally occurring aromatic compound found in the peels of citrus fruits and numerous other plants.

In skincare: Primarily used as a fragrance component.

Important consideration: Limonene can oxidize when exposed to air, producing oxidation products that may increase sensitization potential in susceptible individuals.

Linalool

Type: Monoterpene alcohol

A naturally occurring fragrant compound found in many plants and essential oils.

In skincare: Primarily functions as a fragrance component.

Important consideration: Like limonene, oxidized linalool can have greater sensitization potential than the freshly distilled compound.