The skin is made up of several layers.

The most important layers are:

• the epidermis (outer or upper layer)
• the dermis (inner or lower layer)

The epidermis is mostly made up of flat, scale-like cells called squamous cells. Under this layer are round cells called basal cells. The lower part of the epidermis also contains melanocytes, the cells that make the pigment (or color) called melanin.

The dermis contains:

• blood vessels that carry blood and oxygen
• lymph vessels that carry a fluid with cells that help fight disease
• hair follicles, the space containing the root of a hair
• sweat glands
• sebaceous glands, the glands that produce sebum, which is an oily substance that keeps the skin moist

What Is a Mole?

Sometimes, groups of melanocyte cells (in the upper layer of skin) join with tissue around them to form noncancerous growths called moles. Doctors also use the word nevus (NEE-vuhs) for a mole; the word nevi (nee-VIE) means more than one nevus.

Moles are very common and most people have anywhere from 10 to 40 moles. They may look pink, tan, brown, or any color that is similar to the person's own skin color. Moles can be flat or raised above the skin surface. Most moles are round or oval and smaller than a pencil eraser. People can be born with a mole or it may appear later, usually before the age of 40. When a mole is surgically removed, it usually does not return.