Every person has about twenty-five nevi on their skin. We are used to having all sorts of moles or hyperpigmentation, particularly if we have had them 'forever'. Unfortunately, from time to time we notice new lesions on our body. At such a time, each of us should be extremely vigilant, in particular if we are over 25 or, for example, if we have just returned from a sunny holiday. It turns out that sun exposure can really cause us problems.