Back to Know your nails

Skin undertone

Undertone is the constant hint of colour sitting beneath the surface tone of the skin, and it does not change with a tan: it can be cool, warm or neutral. It is the starting point for choosing a nail shade, because nail colour is always perceived in comparison with the skin around it.

What is the difference between tone and undertone?

Surface tone is the obvious part: whether skin is fair, medium or deep. It shifts through the year with sun exposure. Undertone is the hint underneath, and it stays the same whatever happens. Someone can be considerably more tanned in September than in March and carry exactly the same undertone. That stability is why undertone works as a criterion and surface tone does not.

What are the three, and how are they recognised?

A cool undertone carries a pink, red or slightly blue cast. A warm one leans gold, peach or yellow. A neutral one does not commit clearly either way and is, by a distance, the most common. One point is worth stressing: undertone has no relationship with how light or deep the skin is. There are very fair skins with warm undertones and deep skins with cool ones.

How do you look for it?

In daylight, with nothing nearby to corrupt the reading: no makeup on the hands, no strongly coloured clothing close by, no warm lamp overhead. Three simple observations usually agree. The look of the skin on the underside of the forearm, where sun rarely reaches. Which metal sits better against it, with silver tending to suit cool and gold to suit warm. And how the skin behaves in sun, though that clue is the least reliable of the three.

Why is it so hard to decide?

Because most people are neutral or close to it, and because colour perception depends on context: the same shade reads differently according to the skin it sits on and the light it is seen in. The same forearm looks pink next to orange fabric and golden next to blue. That is why colour is tried against the nail rather than judged in the bottle. Comparison therefore works better than direct observation: hold two polishes of the same hue, one with a cool base and one with a warm base, against the nail and see which leaves the skin looking cleaner.

What does it change about choosing colour?

It changes the base of the shade, not the family. Cool undertones usually sit well with blue-based reds, cool pinks, burgundies, greys and pink-based nudes. Warm undertones read better with corals, orange-based reds, terracottas, creams and peach-based nudes. Neutral undertones take almost anything, which is fortunate and also makes the decision harder through sheer choice.

What if the result still looks slightly off?

Before writing off a colour, try taking the intensity down. Most mismatches come not from picking the wrong family but from a saturation too high for the contrast between that nail and that skin. The same hue muted, or in a matte finish, usually resolves the feeling that something is not quite sitting right without changing colour at all.

Sources: Spanish Academy of Dermatology and Venereology (AEDV) · AEMPS · Cosmetic products (Spanish Medicines Agency)

Published: 12 October 2026 · Last reviewed: 12 October 2026