Do you know what the biggest organ in your body is? It’s not your brain, and it’s not your large intestine. Give up? The subject may have given the answer away, so I’ll suspend any further guesswork and tell you: It’s your skin. That’s right; your skin is an organ (just like your heart, lungs, and liver).

And if you spread out the skin of the average adult it would measure 20 square feet, about the size of a twin-sized bed sheet! In here, I cover the ins and outs of your skin so that you can see just where your acne originates. I acquaint you with the many functions that your “largest organ” performs and tell you a little about how to take care of it.

Your Largest Organ

You may not really think of the skin as an organ, like the heart and lungs. To many people, skin seems more like a simple cover to prevent their insides from falling out. An organ is a somewhat independent part of the human body that performs a specific function. Once you know that, you can see that the skin is an organ, because it performs the following specific functions (in addition to others):

• Protects your body from infection

• Serves as a waterproof barrier between you and the outside world Shields you from the sun’s harmful rays

• Provides cushioning like a shock absorber that defends you from injury D

• Insulates your body and keeps your temperature right around a cozy 98.6 degrees Fahrenheit (37 degrees Celsius)

• Acts as an energy reserve

• Alerts you to potential harm through your sensations of touch and pain

• Repairs itself (that’s why cuts heal)

• Produces vitamin

Because your skin has so many functions, you may not be surprised to discover that it also has a rather complicated structure with many working parts. It contains hairs that have their own oil glands and tiny muscles — I’ll bet that you didn’t know that hairs have muscles!

Your skin has sensory nerves — hot, cold, touch, and pressure receptors. It also is home to blood vessels, lymph vessels, and sweat glands. Plus, your skin has microscopic pigmentproducing cells, cells that work on your immunity, as well as cells that protect and replace themselves.

With all that going on, you may be surprised that your skin doesn’t have its own zip code. Human skin is made up of three layers. First come the top two layers — the epidermis (the outside layer of skin that you can touch and see) and the dermis (which is located directly beneath the epidermis).

Then comes the third, bottom fatty layer that the epidermis and dermis rest upon, which is called the subcutaneous layer. The prefix epi means “upon” and derm means “skin,” so, together, they form epidermis (upon the skin).

And obviously, dermis means “skin.” The prefix sub means “under” and cutaneous is another reference to “skin,” so the word subcutaneous means “under the skin.” (I guess they should have named it the “subdermis” if they wanted to be totally consistent.) In the sections that follow, I take you on a guided tour of each of these layers. And like any good tour guide, I provide you with a map in Figure 1.

The Latin term for cells is “cytes.” Therefore, keratino-cytes, by definition, are cells (cytes) comprised of keratin. Just as your skin has more then one layer (epidermis, dermis, and subcutaneous layer), the epidermis itself has three layers. Within these layers, there’s constant cellular motion going on.

• Outer layer: The outermost layer of the epidermis is known as the stratum corneum, also known as the horny layer. This layer provides your body with a durable overcoat that protects deeper cells from damage, infection, and from drying out.

This layer of your skin is actually made up of dead skin cells. (Your hair and nails are made of dead cells too!) So when you look at your skin, you’re really seeing skin that is dead. But these deceased skin cells only stick around for a little while.

Soon, they flake off — like when you wash, scratch yourself, go shopping, sit in class, fall asleep, and even read this blog. Basically, all the time. In fact, every minute of the day we lose about 30,000 to 40,000 dead skin cells off the surface of our body.

• Middle layer: This layer is known as the stratum spinosum. The cells in this layer looked kind of spiny to the scientists who first described them.

• Inner layer: Known as the basal layer, the inner layer is like a production facility for the new skin cells (keratinocytes) that eventually make their way up through the stratum spinosum to the outer stratum corneum to replace the dead older cells you lose from the surface.

The keratinocytes in the basal layer stand up like little soldiers at attention on what’s called the basement membrane, a barrier that separates the epidermis from the dermis; it’s the anchor that joins the epidermis and dermis together.

The keratinocytes are kept alive by the underlying dermis — which serves as their blood supply because the epidermis has no blood supply of its own. But their upward journey carries them farther away from their supply lines, and as they approach the top, they begin to die.

By the time they’ve reached the outer layer of the epidermis, they’ve lost virtually all of their cellular contents except for tough keratin fibers and other solid proteins. Even as they dry up and die, they become much more resilient and durable and become the flattened cells that form the stratum corneum.

This one-way trip takes about two weeks to a month to accomplish. Figure 2 demonstrates the process. When an injury or an acne pimple penetrates the basement membrane, a scar may result.

Also located in the dermis is the hair follicle (refer to Figure 1). A hair follicle is a hair-containing canal; a tube-shaped sheath that surrounds the part of the hair that is under the skin. It’s located in the epidermis and the dermis. Blocked hair follicles are often at the root of the acne problem. Styes, boils, shaving bumps — I could go on and on — all have their origins in the hair follicle.

Your subcutaneous layer

Fat cells known as lipocytes reside in the subcutaneous layer. Our visit to the subcutaneous layer will be brief because as far as acne is concerned, there’s not much action going on here.

But if you’re interested, your subcutaneous layer is what your outer layers of skin rest upon. Your fatty layer is your body’s insulator, cushion, and natural shock absorber (and it also helps to keep the diet industry in business!).

The subcutaneous layer contains arteries, veins, lymph vessels, and nerves that are larger than those found in your dermis. If you go any deeper, you’ll come upon muscles and possibly some of your inner organs. That’s out of bounds! So I’ll end the anatomical tour right here in Fat City.

Taking Care of Your Skin

Different people and different skin types need to do different things for their skin. We have an old expression in dermatology that still rings true: “If it’s dry, wet it; if it’s wet, dry it.” In recent decades, another truism has been added: “If it’s fair, shield it; if it’s dark, you’re probably very fortunate.”

That’s because your melanin protects you from skin cancers, wrinkling, and keeps you looking young. If your skin is fair, if you burn easily, or if you have a personal or family history of skin cancer, you should protect yourself from the sun by wearing hats and caps, using sunscreens, and avoiding going to tanning parlors.

If your skin is dark, you may have other reasons to protect it from the sun. People with dark complexioned or Asian skin may have other reasons to be very sensitive and prone to irritation and possibly less tolerant of many of the topical medications that are used to treat acne.

The ultimate operating instruction: Whether you have dry, regular, or oily skin, a big acne breakout or smooth sailing on the pimple front, there’s something that’ll keep your face looking its best and most attractive to the rest of the world and is guaranteed to help you make friends and influence people. I suggest that you simply exercise your muscles of facial expression — and smile!

Washing your face

Rocket science? Maybe not. But as a dermatologist, I have a few reasons for walking you through a little face-washing tutorial. First, I often begin my instructions for applying medications in later articles with phrases like “Wash your skin . . .” or “To a clean, dry face, apply . . .” so, it seemed to make sense that I fill you in on the details.

The second reason for this bit of Face Washing 101 is even simpler — many people screw it up. But don’t worry: I’m here to help. And, if you’re like many folks, my face-washing routine can simplify your mornings and evenings and save you some cash. These days, society as a whole is really into soap — the cleaner the better!

As little kids, we’re told to scrub, scrub, scrub with plenty of soap and water. As teenagers, we use more soap — to fight acne and oily skin. As adults, we tend to follow the same routines even though our skin has changed. And the range of different types of soaps available is mind boggling — super-fatted, deodorant, rejuvenating, oatmeal, avocado, citrus, aloe vera, sandalwood, wintergreen, peppermint, patchouli, and vitamin E to name a few.

Many types of cleansers are also available. Some exfoliate as they clean, and the medicated ones generally contain benzoyl peroxide or salicylic acid in various concentrations. Overcleansing with these products can be irritating.

More often than not, these items will only dry out and irritate your skin, particularly if you’re already applying a topical anti-acne medication. Washing excessively — more than twice a day — with any soap (regular soaps, acne soaps, antibacterial soaps, soaps with abrasives, or even gentle soaps) has little positive impact on your acne.

In fact, if you have acne, your skin may be red and inflamed, and frequent washing only makes it redder. Washing your face with a mild soap just twice a day is the best tactic, regardless of your skin type or acne activity. I recommend the following soaps and cleansers, depending on your skin type.

These tried-and-true recommendations may not sound as exciting as a Provencal honey-lavender soap with grape seeds, but they flat out work:

• Oily skin: Ivory soap.
• Dry skin: Dove soap.
• Extra-sensitive skin or allergic reaction to soaps: Nonsoap cleanser such as Cetaphil, Aquanil, or Neutrogena Extra Gentle Cleanser.

At the risk of sounding like a parent — with the whole “wash behind your ears” thing — now that you have your soap, here’s how to use it:

1. Get the soap wet, using lukewarm water.

2. Using your fingertips or a soft washcloth, apply the soap to your skin and rub it gently into your skin using a circular motion. Don’t use loofah sponges, brushes, or sandpaper please.

3. Splash your face with lukewarm water until the soap is completely gone. Expect to rinse your face for just a few seconds — perhaps as long as it would take to sing “Happy Birthday.”

4. Pat — don’t rub — your skin until it’s dry. Use a soft cotton towel.

And that’s it!

Dealing with dry skin

If you have overly dry skin (known as xerosis in the medical world), it’s probably more of a problem for you when the weather is cold and the humidity is low. This occurs most often in the winter months in northern climates. In Western societies, our modern lifestyles also emphasize overbathing, which only serves to worsen the dryness.

On top of that, we often live and work in overheated spaces. If your skin is dry, keep it moist by using only mild soaps or soap substitutes as I recommend in the preceding section. You could also consider moving to a more humid climate — think rain forest.

If you’re already using a mild soap (and assuming a move to the Amazon is out of the question), apply moisturizers regularly, particularly when your skin is still damp. Finding the right moisturizer for your skin may involve trial and error. Look for those that are labeled as noncomedogenic.

I happen to recommend Oil of Olay, but many other excellent products are available. Go ahead and use a moisturizer that contains a sunscreen if you think you need one. You can also use room humidifiers to help hydrate your skin. If you have acne and dry skin, you probably know that acne treatments can make your dry skin worse.

Using moisturizers over your topical acne medicine can make these symptoms more tolerable. If you wear makeup, you can apply it over the moisturizer. Some common recommendations for dry skin are of questionable or no value, including the following:

• Ingesting copious amounts of water
• Taking lots of vitamins

These “remedies” won’t hurt you, but don’t look to them to cure your dry skin. Instead, treat your acne and dry skin with TLC and the gentlest of cleansing methods. If your skin gets flaky and scaly, that doesn’t mean that you have wrinkles. In fact, several of the topical treatments can cause your skin to look dry and scaly as a side effect, but some of these medications can actually prevent wrinkles.

Coping with an oil glut

If you have excessively oily skin, that’s due to your sebaceous glands producing more sebum than you’d like them to. This is often the case if you also happen to have acne. But for now, here are some tips on caring for your oily skin:

• Be happy that you’ll save a few bucks on not buying moisturizers.

• Be happier because your skin will tend to stay more wrinklefree and younger looking!

• Be even happier because your skin will tend to be less sensitive!

But you probably want some more concrete tips, so here you go:

• Even though your skin’s oily, don’t irritate it. Washing your face twice a day should be enough. I realize that you may have been told to wash 77 times a day with strong abrasive soaps, but that will only irritate your skin and make it redder — and if you have acne, all that scrubbing will only make it look worse!

• If parts of your face feel oily during the day, the oil can be wiped away with a mild alcohol-and-water astringent such as Neutrogena Clear Pore Oil-Controlling Astringent, Noxzema Triple Clean Astringent, or Clean & Clear Advanced Acne Pads.