Keratosis is a benign elevated skin growth, usually a brown-reddish colour, which tends to form a crust. It is caused by the alteration or proliferation of keratinocytes and consequent thickening of the stratum corneum, i.e. the superficial layer of the epidermis. Keratosis is more common in people with fair skin and its onset usually occurs in midlife, mainly in the areas most exposed to sunlight. In rare cases, keratosis can evolve into a malignant form, therefore regular check-ups are recommended.