Habits, both good and bad, often show up on our skin. A love of the great outdoors may result in sunburn or blisters, while an addiction to late-night TV watching may show up in the form of under-eye circles. Smoking has such a profound effect on the skin that researchers have coined the phrase "smoker's face." Sexual activity can lead to genital warts and herpes. An allergy to food or medication can result in in rashes and other skin conditions. All these things can reveal themselves on the skin's surface.

Smoking and skin

Though the creators of those cigarette advertisements with glowing, youthful models would have us think otherwise, smoking wreaks havoc on the skin.

Nicotine diminishes blood flow and prevents skin tissue from receiving the oxygen it needs. This results in "smoker's face", a premature aging of the skin characterized by deep wrinkles, especially around the mouth, gaunt facial features, and a wasted, gray coloration. The hands of smokers are often marked by a yellow-brown discoloration of the fingernails.

Other skin conditions linked to smoking include skin cancer and psoriasis, a chronic skin disorder characterized by dry, scale-covered red patches on the scalp, ears and genitalia. According to the American Academy of Dermatology, smokers with melanoma (a particularly deadly form of skin cancer) are at greater risk of dying from the cancer than are non-smokers.

Diet and skin

Our diet can have an impact on our skin. Skin reactions such as eczema, hives and itching can warn us of allergies to such foods as eggs, peanuts or red wine. Skin can also uncover a severely restricted diet. Dry skin covered with fine hair, rashes, and pimples -- among other skin conditions -- can be a tell-tale sign of an eating disorder, such as bulimia.

Sexual activity and your skin

Through sexual activity, you may become infected with genital warts or herpes, conditions which not only may be very uncomfortable but may also signal more deep-seated health problems. If you are sexually active, make sure you are tested for sexually transmitted diseases (STDs) regularly.

Outdoor activity and your skin

A day spent hiking in the great outdoors and a night sleeping beneath the stars can be heaven -- or hell. Blisters, sunburn, insect bites, and skin reactions to poison ivy or poison oak can detract from even the most breathtaking scenery

Sleep and your skin

Sleepless nights can take their toll, resulting in puffy eyes and dark under-eye circles. Makeup and under-eye treatments may provide some cover, but there is no substitute for a good night's sleep.