When you were in grammar school you probably learned the names of the major organs of the body: "heart," "lungs," "colon," "liver," " kidneys," ort"brain." There are, of course, other important organs that can be added to that list. But most people would probably neglect adding the biggest, most visible and one of the more important organs of the body: "skin."

If your skin could be laid out on a table it would cover about 18.2 square feet and weigh approximately six pounds. This strong waterproof sack is your body's first line of defense. It projects bones and other organs, perspires to help eliminate waste, cools us when we are hot and produces an oily secretion that plays a significant role in providing a barrier against anything that attempts to invade it. It has a rich supply of sensitive nerve endings that respond to touch and temperature to help us navigate through our environment.

Skin varies in thickness. It is thinnest on the eyelids and thickest on the palms of our hands and the soles of our feet. Continuous pressure over any part of the skin causes it to thicken, creating a callus for additional protection.

Healthy skin is slightly moist, soft, flexible and free of disease. Its texture is smooth and its color, which varies depending on the amount of pigment it contains, looks healthy. It is elastic, resilient, and, when we were young it renewed it every 28 to 30 days. By the time we age into our sixties, skin turnover has declined and it can take up to fifty days to renew itself.

Most important of all may be the role skin plays as a mirror to you and the outside world. When we are well nourished, in good physical shape, emotionally stable, well rested and keeping our skin clean and moisturized, it glows. The opposite is also true.

As we age there are many changes to our body. Our large visible organ, skin is no exception. Aging skin:

• gets drier: the sebaceous (oil) glands decrease production-that's why we need to use moisturizer.
• gets thinner: subcutaneous fat shifts leaving surface skin thin-that's why we bruise more easily.
• doesn't respond as quickly to injury: the healing process is slower-scratches and cuts heal more slowly than the same injury to a grandchild.
• is less able to regulate temperature: sweat glands don't work as well so your body doesn't adjust as quickly to changes in temperature.
• doesn't respond to sun; cells that produce melanin don't work as well so your ability to fight sun damage is decreased, producing uneven skin color.

Signs of aging skin include:

• age spots
• circles under eyes
• puffy eyes
• drooping eyelids
• lines and wrinkles
• sagging skin
• skin cancers
• skin tags
• uneven texture
• uneven skin tone
• dull appearance

There are controllable and uncontrollable factors that affect the quality of our skin.

Controllable factors include;

• alcohol: the less the better
• cigarettes: terrible for facial skin
• diet: especially unbalanced diets)
• dehydration: water, water, water
• emotional health; meditate
• exercise habits; challenge yourself daily
• (harsh) skin care products
• pollution; avoid it
• sleep deprivation: 7-8 hours night
• stress: respond vs. react
• sunshine: use sunscreen

Uncontrollable factors:

• aging
• disease
• facial expressions
• gender
• genetics
• gravity
• hormone shifts
• injuries
• photosensitivity (photo-toxic) reactions

Most of the triggers in the above list are self-explanatory. Photosensitivity-not so much! Medication induced sunburn is the short explanation for describing photosensitivity. It's typically divided into phototoxic and photoallergic reactions. A phototoxic reaction occurs on sun-exposed skin only. It happens soon after sun exposure. Photoallergic reactions, which occur less often, is not so immediate but can spread to areas that weren't exposed to the sun. They trigger "rash-like and occur from one to three days after sun exposure.

If you sunburn easily, chances are some medications will trigger this photoallergic or photosensitive response. It can range from mild sunburn with any sun exposure to the blistering and oozing that's typical of severe sunburn to reactions that resemble a breakout of hives or eczema.

The most commonly known prescription medicines that trigger sun sensitivity are antibiotics. However medicines to treat acne, drugs that treat cancer, anti-depressants, anti-fungals, diuretics, antipsychotics, antihistamines, and diabetes medications are also culprits for what doctors call a phototoxic reaction. Carefully read all the labels on your prescription bottles for this information.

Take herbs for health? Buyer beware. Medicines that help can also harm and herbs are no exception when it comes to sun-sensitivity. Other culprits include perfumes, deodorants, dandruff shampoos and bar soaps that contain quinolone, bergarnot oil and sandalwood oil. If you use any of these it's mandatory you take extra protection when in the sun-especially our hot Arizona sunshine.

I live in Arizona, where sun is prevalent, intense and a year-round certainty. Understanding how it affects skin is mandatory. But no matter where you live, sun damage is a reality. Take care.