# Skincare ingredient library

> Source: https://thecastindex.com/beauty/ingredients — updated 2026-09-25

Plain-English fact sheets for common skincare ingredients, each linked to catalogue products that list it. General information, not medical advice.

- [Niacinamide](https://thecastindex.com/beauty/ingredients/niacinamide) — Vitamin. Niacinamide is a form of vitamin B3 used in serums, moisturisers, sunscreens and tints. Studies associate it with a more even-looking tone, less visible redness and blotchiness, and support for the skin barrier. It is generally well tolerated, which is why it appears in so many everyday formulas.
- [Retinol and retinal](https://thecastindex.com/beauty/ingredients/retinoids) — Vitamin A derivative. Retinol and retinal (retinaldehyde) are vitamin A derivatives used in evening skincare. They are among the best-studied ingredients for the appearance of fine lines, uneven texture and tone. Retinal is one conversion step closer to the active form than retinol. Both can irritate at first, so build up slowly.
- [Vitamin C](https://thecastindex.com/beauty/ingredients/vitamin-c) — Antioxidant. Vitamin C is an antioxidant used in serums to help skin look brighter and more even, and to support protection against environmental damage alongside sunscreen. Pure L-ascorbic acid is the most studied form but the least stable; derivatives are gentler and more stable, though evidence for them is more limited.
- [Hyaluronic acid](https://thecastindex.com/beauty/ingredients/hyaluronic-acid) — Humectant. Hyaluronic acid is a humectant: it attracts and holds water, helping skin feel and look more hydrated and plump. The body makes it naturally, and cosmetic formulas often combine several molecular sizes. It suits almost every skin type and works best under a moisturiser that seals hydration in.
- [Ceramides](https://thecastindex.com/beauty/ingredients/ceramides) — Barrier lipid. Ceramides are fats (lipids) that make up much of the skin’s outer barrier. Moisturisers and cleansers add them back to help skin hold water and resist dryness and irritation. They are especially useful for dry, sensitive or over-exfoliated skin and are among the least likely ingredients to cause problems.
- [Peptides](https://thecastindex.com/beauty/ingredients/peptides) — Signal and conditioning molecules. Peptides are short chains of amino acids. In cosmetics they are used to condition skin, lips, lashes and hair, and some are marketed as “signal” peptides for the look of firmness. Evidence varies widely between specific peptides, so treat broad claims cautiously and judge each formula on its full ingredient list.
- [Exfoliating acids (AHA and BHA)](https://thecastindex.com/beauty/ingredients/exfoliating-acids) — Chemical exfoliant. Exfoliating acids loosen the bonds between dead skin cells so they shed more evenly. Alpha hydroxy acids (AHAs) such as glycolic and lactic acid work on the surface for smoother, brighter-looking skin; beta hydroxy acid (BHA), salicylic acid, is oil-soluble and works inside pores, which suits oily and blemish-prone skin.
- [Centella asiatica (cica)](https://thecastindex.com/beauty/ingredients/centella-asiatica) — Botanical. Centella asiatica, often shortened to “cica”, is a plant extract widely used in Korean skincare to soothe and calm skin. Its active compounds, such as madecassoside and asiaticoside, are studied for wound-healing and anti-inflammatory properties, and cosmetic formulas use it to comfort stressed or irritated-feeling skin.
- [Sunscreen filters (UV filters)](https://thecastindex.com/beauty/ingredients/sunscreen-filters) — UV protection. Sunscreen filters absorb or reflect ultraviolet light. SPF measures protection against UVB, the main cause of sunburn; UVA protection is shown by a UVA logo or star rating in the UK and by PA ratings on Korean and Japanese products. Mineral filters (zinc oxide, titanium dioxide) and modern chemical filters can both protect well.