Freckles are clusters of concentrated melanin which are most often visible on people with a fair complexion. A freckle is also called an ephelis. Freckles do not have an increased number of melanin producing cells (melanocytes), but instead have cells that overproduce melanin granules changing the coloration of the skin. This also causes the different skin tones among humans, but contrasts to lentigines and moles.
Freckles can be found on anyone no matter their genetic background; however, the number of freckles is genetic and is related to the presence of the melanocortin-1 receptor MC1R gene variant. The formation of freckles is triggered by exposure to sunlight. The exposure to UV-B radiation activates melanocytes to increase melanin production, which can cause freckles to become darker and more visible.
Freckles are predominantly found on the face, although they may appear on any skin exposed to the sun, such as arms or shoulders. Heavily distributed concentrations of melanin may cause freckles to multiply and cover an entire area of skin, such as the face. Freckles are rare on infants, and more commonly found on children before puberty. Upon exposure to the sun, freckles will reappear if they have been altered with creams or lasers and not protected from the sun, but do fade with age in some cases.
Freckles are not a skin disorder, but people with freckles generally have a lower concentration of photo protective melanin, and are therefore more susceptible to the harmful effects of UV radiation. It is suggested that people whose skin tends to freckle should avoid overexposure to sun and use sunscreen.
Ephelides describes a freckle which is flat and light brown or red and fades with reduction of sun exposure. Ephelides are more common in those with light complexions, although they are found on people with a variety of skin tones. The regular use of sunblock can inhibit their development.
Liver spots (also known as sun spots and lentigines) look like large freckles, but they form after years of exposure to the sun. Liver spots are more common in older people.