The Skinny on Skin

* A typical square inch of body skin includes about 19 million cells, including an average of 625 sweat glands, 90 sebum or oil glands, 65 hair follicles, 19,000 sensory cells and about 12 to 13 feet of microscopic blood vessels.

* Goose bumps are caused by smooth muscles that are concentrated around hair follicles. Under stimulation these muscles contract. This can be a reaction to cold or an evolutionary “flight or fight” response.

* Every day we shed billions of dead skin cells and about 200 body hairs.

* Skin pales as we grow older because the blood vessels under the skin thin out. This blood vessel loss may also explain why older people feel cold easily.

* Even the fragile-appearing skin of a child is tough. To tear skin requires 25 pounds of force applied laterally.

* Americans spend 6% to 10% of their expendable income on cosmetic products.

* On any given day, only about 50 to 100 follicles are actively involved in hair production.

* In a 140-pound person, skin weighs about 22 pounds, or 16% of body weight, and accounts for 5% to 8% of the body’s metabolic demand.

* A fetus generally forms no scar tissue after injury or incision. This may be due to the fact that the fetus generates very low levels of substances called cytokines that excite inflammation.

* That burning sensation from a sunburn is due to the blood vessels opening up and allowing plasma to leave the blood and bloat the tissues.

* The increased rate of melanoma--812% over the last five decades--is by far the largest increment recorded for any cancer type.

* Female and male smokers 40 and older are two to three times as likely to have moderate to severe wrinkling compared with nonsmokers.

Source: “The Body’s Edge: Our Cultural Obsession With Skin,” (Henry Holt) by Marc Lappe.