Glossary from A to Z.

A

AHA (alpha hydroxy acids)

Water-soluble acids such as glycolic and lactic acid that loosen dead skin cells on the surface. They make skin smoother and more even but can irritate. Don't use on the same evening as retinoids, and always wear sunscreen the next morning.

B

BHA (salicylic acid)

Oil-soluble acid that gets into oily pores and keeps them clear from within. Good for blemishes, blackheads and enlarged-looking pores. Start on 2 evenings a week, then build up to every other evening.

Related studies: Arif 2015

C

Ceramides

Lipids found naturally in skin that sit like mortar between skin cells. In creams they support the skin barrier, especially for dry and sensitive skin.

Combination skin

Skin that's shiny on the forehead, nose and chin but normal or dry on the cheeks. Skinpaired places it more precisely on the “oil” axis.

Comedogenic

Describes ingredients that are more likely to clog pores. Whether a product clogs your pores depends a lot on the whole formula and your skin.

D

Dark spots

Darker areas from extra melanin, for example after sun or after spots. Daily sunscreen is the basis; niacinamide and vitamin C can improve the look.

Related studies: Hughes 2013, Bissett 2005

Double cleanse

Two cleansing steps in the evening: first an oil, balm or micellar water to dissolve sunscreen and make-up, then a gentle cleanser. Worth it with daily sunscreen or make-up.

F

Fragrance (parfum)

Substances that make skincare smell nice. They're among the more common triggers of skin reactions. In the ingredient list they appear as “Parfum” or “Fragrance”, sometimes with individual substances like linalool or limonene.

Related studies: Diepgen 2016

G

Glycerin

One of the most proven humectants. Inexpensive, well tolerated and near the top of the ingredient list in many creams.

H

Humectants

Substances that bind water and hold it in the skin, such as glycerin, hyaluronic acid, panthenol and urea. They're the basis of almost every moisturiser.

Hyaluronic acid

Binds many times its weight in water and plumps the skin surface. Works with all actives. Best applied to slightly damp skin and sealed with a cream.

Related studies: Pavicic 2011

I

INCI

The internationally standardised ingredient list on cosmetics. Ingredients are listed in descending amount; those under 1 % may appear in any order.

M

Micellar water

Cleansing water with tiny surfactant spheres that pick up make-up and dirt. Good as the first step of a double cleanse.

N

Niacinamide

A form of vitamin B3. Can reduce shine, the look of pores, red blotchiness and dark spots, and is usually well tolerated. Works morning and evening, also with retinoids and vitamin C.

Related studies: Bissett 2005, Draelos 2006

O

Occlusive

Ingredients that form a film on the skin and slow evaporation, such as petrolatum, shea butter or squalane. Good as the last step for dry skin.

Order (layering)

The order of products: from watery to rich. Cleanse first, then active, serum, cream and, in the morning, sunscreen last. That way every step works.

P

Panthenol

Pro-vitamin B5. Hydrates, soothes and supports the skin barrier. Common in creams for sensitive skin and for after shaving.

Related studies: Proksch 2017

Patch test

Testing a new product on a small area, such as the neck or behind the ear, for a few days before using it on the whole face. Always introduce only one new product at a time.

Related studies: Diepgen 2016

pH

Skin is slightly acidic, around pH 4.5 to 5.5. Gentle cleansers with a skin-like pH dry the skin out less than classic soap.

PHA (polyhydroxy acids)

Acids such as gluconolactone with larger molecules. They work like AHAs but penetrate more slowly and are considered gentler.

Purging

Temporarily more blemishes in the first weeks with retinoids or acids, because skin renews faster. If it lasts longer than about six weeks or your skin burns, go back a step.

R

Retinal (retinaldehyde)

A form of vitamin A that's one conversion step closer to the active form in the skin than retinol. Works on fine lines and evenness and is often well tolerated. Use in the evening with a step-up phase.

Related studies: Creidi 1998

Retinoids

Umbrella term for vitamin A derivatives such as retinol and retinal. In cosmetics they're well studied for fine lines and smoother skin. Never on the same evening as acids, and always sunscreen in the morning.

Related studies: Kafi 2007, Creidi 1998

Retinol

The best-known form of vitamin A in cosmetics. In the EU, face products may contain at most 0.3 % retinol equivalent. Beginners start at a low strength and increase slowly.

Related studies: Kafi 2007

S

Sebum

The skin's own oil from the sebaceous glands. Too much makes skin shiny and clogs pores; too little makes it dry. Every Skinpaired profile starts on this axis.

Related studies: Draelos 2006

Serum

Light, usually watery skincare with one focus, such as hydration or an active. Goes on after cleansing and before cream.

Skin barrier

The top layer of the skin, made of skin cells and lipids such as ceramides. It keeps moisture in and irritants out. When it's disrupted, skin feels tight, stings or flakes more easily.

Related studies: Proksch 2017

SPF (sun protection factor)

Shows how strongly a product protects against UVB rays. For everyday face use, Skinpaired recommends SPF 50. Enough product and broad-spectrum protection that also covers UVA are what matter.

Related studies: Hughes 2013

Squalane

A light, stable oil similar to the skin's own lipids. Nourishes without a heavy film and is well tolerated by many skin types.

Step-up phase

The period in which a strong active is slowly increased, for example first on 2, then on 3 evenings a week. This lets the skin adapt and makes redness or flaking less likely.

Related studies: Kafi 2007

T

TEWL

Transepidermal water loss: how much water evaporates through the skin. A measure of the skin barrier used in many skincare studies.

Related studies: Proksch 2017

U

Urea

A natural moisturising factor of the skin. At low strength it hydrates; at higher strength it softens rough patches.

UV filters (mineral and chemical)

Mineral filters such as zinc oxide and titanium dioxide scatter and absorb UV light; chemical filters absorb it. Modern sun fluids often combine both for light textures without a white cast.

Related studies: Hughes 2013

V

Vitamin C

Antioxidant that, under sunscreen in the morning, buffers UV-related stress and makes the complexion look fresher. Pure ascorbic acid is sensitive to light and air; derivatives are more stable and milder.

Related studies: Telang 2013

Z

Zinc PCA

Zinc compound used in serums for shiny skin, often combined with niacinamide.