A freckle is a small, flat, tan or light brown spot on the skin, usually appearing on the face, shoulders, and arms. Freckles show up most often on people with lighter skin, especially those with red or blonde hair, and they tend to multiply and darken with sun exposure during summer months.

Freckles form when sunlight triggers certain skin cells to produce melanin, the pigment that gives skin its color. Unlike moles, which are often raised and tend to stay the same year-round, freckles are flat and often fade during winter when you're spending less time outdoors. Some people have just a few scattered across their nose, while others have hundreds dusting their entire face and arms.

While some kids feel self-conscious about their freckles, many cultures consider them distinctive and attractive. Freckled simply means covered with freckles. Famous freckled faces throughout history include Mark Twain and mathematician Alan Turing. Scientists have discovered that freckles are hereditary: if your parents have them, you're more likely to have them too. Whether you have freckles or not, they're simply one of the many ways human skin responds uniquely to sunlight.