Getting Under the Skin ; The Body’s Outer Layers Are Its First Line of Defense Against Disease

It’s all around you, literally. All 25 square feet or so.

It’s the largest organ in your body, weighing in at about 8 pounds.

It’s your skin.

Over the next 27 days, you will shed all of its 7 billion cells, which will flake away unnoticed, an amount equivalent to 1.5 pounds in a year. Plump, new cells will percolate from the skin’s inner layers to the surface.

You will do this repeatedly and become an entirely changed person almost 1,000 times throughout a normal life span, at least on the outside.

“The skin does a ton of amazing things,” said Dr. Lawrence Eichenfield, a pediatric dermatology specialist at Children’s Hospital and Health Center at the University of California San Diego School of Medicine.

Besides keeping blood and tissue inside the body, the skin orchestrates its dozen layers and sublayers to protect the body against invasion from outside forces, such as germs, blunt objects, corrosives, bugs and the weather.

Markings – moles, fingerprints, freckles, pigmentation, dimples, scars, hairiness (or lack of it) and even lines and wrinkles – give each person a unique appearance.

Cells in the skin’s three primary layers – the epidermis, dermis and subcutaneous – usually seem to know precisely what they should let inside, such as an increasing number of medications applied by patch or cream, and what to keep out, such as caustic metals and irritants.

They seem to know what to let out as well, such as salty water to cool the body when it gets too hot, and oils from glands embedded in the skin when the air is dry to keep the skin from drying out.

Skin protects a fragile network of 45 miles of tiny nerves, and in every square inch cells are entwined with 625 sweat glands.

It tingles, itches, blushes and throbs. It gets goose bumps when it is cold or when a person is scared. And when the skin is hurt, it stings and bleeds and scabs and scars.

With calluses, extra layers of skin provide protection from repetitive stress, such as the bulge on the middle finger from using a writing utensil all day.

Skin also stores energy and fat and synthesizes vitamin D, vitally necessary for the entire body. Skin protects against constant friction from everyday contact with chairs and beds and general wear and tear. It changes appearance and color when we aren’t getting the right nutrition.

“As doctors, we have the advantage with skin of seeing with the eye more of what’s going on inside the body than we can with internal organs,” Eichenfield said.

But along the way, a few things can and usually do go wrong with our skin. Eichenfield, a pediatrician, said that for every job that skin cells do right, there are examples seen in infants and children of how they fail.

“We learn how normal functions are supposed to work by seeing how they don’t work,” he said.

An example is skin of newborns that grows too thin or too dry at first. Sometimes, the genes regulating the normal anchors that hold the skin down are missing in infants, as in a tragically disfiguring but rare disorder called epidermolysis bullosa. The skin constantly blisters, and the wounds don’t heal.

Assault from sunlight can cause cancers, overactive cellular turnover provokes psoriasis, and allergic reactions to detergents, metals or other environmental chemicals can cause inflammation leading to eczema.

Genetic mutations can create distressed or weak skin. Environmental toxins from poison ivy to man-made chemicals can cause rashes. And the body’s own immune system can revolt, causing a variety of annoying to disabling conditions.

Such conditions can range from alopecia areata, or hair loss, to lupus, in which antibodies see the skin as foreign and attack it, causing inflammation of blood vessels and rashes when skin is exposed to the sun.

A list of common and rare skin diseases and conditions runs from A to Z – from common acne and athlete’s foot to xerosis and herpes zoster. Some dermatologists say the dictionary of dermatology reads like a Scrabble player’s, with dreadful-sounding terms such as:

* ichthyosis, potentially disfiguring skin flaking and scaling;

* myxoid cysts, clear rubbery nodules usually appearing on the toes and fingertips;

* pityriasis, oval pink patches usually on the back that are probably caused by a virus;

* vitiligo, death of melanocytes, the cells in the epidermis that produce melanin or pigment, causing areas of skin to turn white.

Some San Diego dermatology experts say that in rare cases they treat people with leprosy, a bacteria that attacks nerve cells of susceptible people, mainly small numbers of immigrants who acquired the disease in their native lands.

“I think I can safely say that at some point in everyone’s life, they will have some problem with their skin,” said Dr. Stephen Webster, clinical professor of dermatology at the University of Minnesota School of Medicine in Minneapolis and a spokesman for the American Academy of Dermatology.

“I’m 69, and there’s no one who can live to be that age who hasn’t gotten warts, acne, blisters or wrinkles.”

Unfortunately, Webster said, “we’re big on cholesterol to protect your heart, but we take the skin for granted.”

Every square inch of human skin is home to about 32 million friendly bacteria whose job is to protect their host against its opportunistic cousins: microbes such as bacteria, fungi, viruses, protozoa, amoeba and a variety of yeasts.

Sometimes there is not quite enough to do the job. Certain viruses may get through, causing cold sores or warts, and some varieties of bacteria can keep ordinary wounds from healing. Fungal infections can be unsightly as well as painful.

Certain drugs also can have an effect on skin, causing allergic reactions or rashes.

Then there is the insult of aging.

Hair grows where it isn’t supposed to and doesn’t where it should.

Wrinkles, lines, dark spots and veins creep in, damaging collagen and elastin that give skin its smooth firmness and elasticity.

Gradually, skin appears mottled and worn, a process that has spawned a rapidly evolving and lucrative industry of cosmetic techniques involving everything from creams and abrasives to plastic surgery, chemical peels, lasers and light therapies.

Sclerotherapy agents – fluids including saline – are injected into the skin to collapse spider veins and other forms of varicose veins that are not harmful to health but can be unsightly.

Some conditions can’t be cured, such as psoriasis and eczema.

“But with newer medicines we can control them and make them better,” Bushman said.

Dr. Martin Kabongo, a UCSD clinical professor of family medicine who specializes in skin disorders, said most skin problems are not treated by dermatologists, but by primary care practitioners.

Kabongo said that often is a problem because many family doctors fail to diagnose skin diseases in people of color, whose pigmented skin may mask problems that are much more easily seen in people with light complexions.

Pigmented skin can mask fungal infections such as ringworm in children, for example.

“Pigmented skin has a way of hiding the subtlety of skin changes, such as a mole that may turn out to be a dangerous melanoma,” a lethal form of skin cancer, Kabongo said. “Most people dismiss it as part of a person’s normal color.”

Melanoma accounts for 4 percent of skin cancer cases, but causes 79 percent of skin cancer deaths, according to the American Cancer Society, which estimates about 55,000 patients will be diagnosed with melanoma in the nation this year.

Experts say that with proper sunscreens and early attention to the earliest signs of skin change, most people can protect themselves.

Doctors are looking forward to an onslaught of discoveries of drugs, monoclonal antibodies, gene therapy and techniques such as refined laser technologies that wipe out imperfections and disease and to take years off aging baby boomers.

New medicines for psoriasis target the disease rather than the broader immune system.

“In the next 10 to 20 years, there will be dramatic changes in treatment,” Webster said. “There will be a great deal of genetic research to provide gene therapies to prevent many genetic disorders of the skin that can be so disabling.”