As you enter your 40s and 50s, there's a good chance that you'll see new patches of pigmentation appear on your skin. These are usually called age spots, but are also known as liver spots or solar lentigines. However, it might be more appropriate to simply call them sun spots.
That's because these masses of pigmentation appear on skin that gets the most exposure to sunlight. Age spots are caused by damaging ultraviolet light (UV) from the sun. UV accelerates the production of a dark pigment called melanin. Age spots are actually a defensive reaction from your skin as it attempts to protect deeper layers of flesh. Tanning beds often accelerate the development of age spots.
Age spots are flat, not raised, and can be brown, black or gray in color. They're usually oval in shape and simply look like excessive pigmentation. Most age spots appear on the backs of hands and feet, upper back and shoulders, and face, and they're typically the size of freckles, but often appear in clusters, and thus, seem much larger.
Age spots are harmless. However, they are somewhat similar in appearance to the beginning stages of some skin cancers. If you see a very dark age spot (or one mottled with several colors) with an irregular border or that is getting bigger at a noticeable rate, see a doctor.
As with many skin issues, some people have genetic predisposition to age spots. If you have fair or light skin, or a history of sun burns, you're at a greater risk of developing a lot of noticeable age spots.
Once age spots appear, there are a few ways you can treat them. Bleaching creams can reduce the darkness of the spots, as can laser therapy, chemical peels, dermabrasion or cryotherapy.