CI 77491

CI 77491 is the colour index number for red iron oxide, a naturally occurring mineral compound used as a pigment. The CI prefix stands for Colour Index, an international reference system that gives every approved colourant a number, which is why the name looks so unlike an ingredient.

It belongs to a set of three. CI 77491 is red, CI 77492 is yellow and CI 77499 is black, and blending them in different proportions produces the full range of skin tones. Seeing all three on a label is entirely normal in any tinted product.

Cosmetic iron oxides are produced synthetically rather than mined, which allows tight control over purity and shade consistency. They are among the most stable colourants available: they do not bleed, fade meaningfully in daylight or react with other ingredients, which is why they have been the standard for skin-tone products for so long.

You will find them in foundations, tinted moisturisers, tinted sunscreens, concealers, BB creams, blushers and mineral makeup. They are also very well tolerated, being inert, fragrance-free and non-comedogenic, and they are a common choice in products aimed at sensitive skin.

Their more interesting property is one many people are unaware of. Alongside providing colour, iron oxides block visible light, which ordinary UV filters do not, and that has made tinted sunscreens meaningfully more useful for anyone concerned about the appearance of pigmentation.

As a pigment, iron oxide works by absorbing and reflecting particular wavelengths of light, which is what produces its colour. The particles sit on the surface of the skin rather than penetrating it, and because they are opaque they also provide coverage, evening out the appearance of tone and softening the look of marks and redness.

The photoprotective role works on the same principle applied to a different part of the spectrum. Conventional sunscreens filter ultraviolet light, which is only part of what reaches the skin; visible light makes up a substantial share of daylight and is not blocked by standard UV filters. Iron oxide particles reflect and scatter visible light away from the skin, adding a layer of protection that a clear sunscreen does not provide.

This matters because visible light is known to contribute to pigment formation, particularly in deeper skin tones and in patchy pigmentation of the kind that recurs and spreads. For anyone working on the appearance of uneven tone, a tinted product containing iron oxides worn over or as part of a sunscreen closes a gap that a clear formula leaves open. It is a supporting measure rather than a replacement for broad-spectrum SPF.

Iron oxides are worth seeking out deliberately if pigmentation is a concern for you.

• Choose a tinted sunscreen over a clear one if you are working on the look of uneven tone. Check the ingredients list for CI 77491, 77492 and 77499.
• Apply it as your sunscreen step, as the last skincare layer in the morning, before makeup.
• Use enough. A thin, sheer layer provides less visible-light protection than a properly applied one, and the same applies to the SPF.
• Reapply through the day if you are outdoors, as with any sun protection.
• Heat matters too for patchy pigmentation, so shade and sensible sun habits still count.
• Pairs well with tranexamic acid, niacinamide, alpha-arbutin and vitamin C, which work on pigment from the inside while the tint works from the outside.
• Very well tolerated, inert and non-comedogenic, so it suits sensitive and breakout-prone skin.
• Remove it properly at the end of the day. Pigments and sunscreen benefit from a thorough cleanse.