Hundreds of millions. From Wikipedia: The average square inch (6.5 cm²) of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and more than a thousand nerve endings. Each sweat gland is made of thousands, if not millions of cells. Also, the number of cells per square inch is different for each part of the body. There are a million melanocytes (the cells with pigment that prevent sunburn) per square inch of skin exposed to sun. The skin is constantly shedding dead cells, too. The skin of the human forearm, for example, sheds about 8,400 cells per square inch every hour. What's even more amazing is that a square inch of skin on average has about 500 million bacteria cells on it as well.