Unlike a freckle that darkens upon light exposure, lentigo (pleural:lentigenes) does not. There is a focal increase in melanocytes of the basal layer, along with thinning of epidermis and elongation of rete ridges. Lentigines can occur at any age; those in older persons may be termed senile lentigines or age spots. A nevus typically forms a nodule and likely appears much earlier in life. Loss of melanin is termed vitiligo and is a separate process from melanocyte hyperplasia. A collection of mast cells can produce urticaria pigmentosa, which often has a light brown appearance, but pruritus is common. Some superficial fungal infections (black piedra) may be pigmented, but they typically do not persist for years.