Myth: Why we get white spots on nails

This week Kat's got her finger on the pulse to get to the bottom of why we getwhite spots on our nails...

Kat - We're a glamorous bunch at the Naked Scientists, and while comparing manicures Graihagh noted that she's got quite a few white spots on her fingernails. All of us had a vague memory that they're something to do with calcium deficiency - after all, calcium is good for your teeth and bones, so surely it's good for nails, right? Actually, we were wrong.

There are plenty of folk-lore explanations for white spots - for example, that a white spot means you'll get a present when it gets to the end of your nail, or that the number of white spots on your left hand tots up the number of lies you've told. I've even seen the suggestion that white spots is the result of eating too much mayonnaise! None of these are true, and what's more - white spots have nothing at all to do with calcium. More formally known as leukonychia, white spots in the nails are incredibly common and are the result of damage to the base of the nail - that's an area known as the matrix - rather than any nutritional deficiency. Nails are made up of specialised cells containing large amounts of a sturdy protein called keratin, which grow outwards and form fingernails and toenails. Damage to the matrix prevents newly-formed keratin-packed cells from bonding together properly, leaving a tell-tale white blotch.

This damage could be the result of an injury like a knock or bang - it doesn't have to be slamming your finger in a door, even smacking it on a table could do it - or even an overly-vigorous manicure. But because nails grow so slowly, cranking out just a few millimetres in a month, it can take a good six weeks for a patch of damage in the matrix to grow up and manifest itself as a white spot in the nail. And by that time you've probably forgotten all about the original incident.

Simple white spots are harmless, and will eventually grow out, although this can take up to eight months. Sooooo slow! But your fingernails are actually a useful window on your internal health in many ways, and there are other conditions that can cause more dramatic changes to the shape and colour of fingernails, including arsenic poisoning, chemotherapy for cancer, heart disease, kidney failure, low protein levels in the diet, eczema and psoriasis, and general poor health. For example, if your fingernails turn completely white, you should be worried, because that's a sign of liver disease. And although calcium levels don't seem to have any impact on nails, other minerals do. For example, a lack of iron in the diet can lead to spoon-shaped dips in the nails, while a lack of zinc is also thought to lead to brittle nails and white patches.

Fungal infections can cause brown or pale patches under the nails, and allergic reactions to nail products such as polishes or varnish removers can cause changes and discolouring. And one colour change that you really don't want to ignore is a persistent black or dark brown patch under the nail - especially toenails, and particularly if you have dark skin. That could be a sign of acral melanoma - a rare type of skin cancer, so it's worth getting anything like that checked out by your doctor. And finally, one major cause of damaged patches on the nails is good old-fashioned fingernail-biting, so get those fingers out of your mouth!