If you had skin cancer, would you know it?

For many people, the answer to this question is no. They don't know how to look for signs of skin cancer on their own skin. Because of this, if they get skin cancer, they may not spot it promptly.

Most types of skin cancer can be treated quickly and easily if they are found early. But if the diagnosis is delayed, the cancer can spread. In the case of melanoma, this can be fatal. Even for less serious skin cancers, such as the very common basal cell carcinoma and squamous cell carcinoma, delayed detection can lead to complications.

So how do you spot skin cancer? The key is knowing your own skin and being aware of changes in it.

The best way to do this is to learn how to do a complete skin self-examination. To do this, you need a full-length mirror, a hand mirror, and a place where you can use them in privacy. Stand in front of the full-length mirror and look carefully at the skin on every part of your body that you can see. Get to know your moles, marks, and other skin irregularities. Then, use the hand mirror to help you look at the places on your body that you can't see with just one mirror. Again, take note of any marks that you see.

Once you're familiar with what your skin normally looks like, you'll be prepared to spot changes. Any new change in your skin should be brought to the attention of a doctor, preferably a dermatologist (a doctor who specializes in treating skin problems). Most changes will turn out not to be skin cancer, but it's worth the trouble of having them checked out.

Changes that you should particularly look for, according to the American Academy of Dermatology, include the following:

- A sore that never really heals
- A translucent growth, perhaps with rolled edges
- A dark streak under one of your fingernails or toenails
- A cluster of shiny pinkish or reddish areas that grows slowly
- A scar with a waxy feel to it
- A flat or slightly depressed area that feels hard

When you're looking at your skin, it's especially important to examine all moles carefully. Most moles are perfectly normal, but it's possible for an unusual-looking mole to be a melanoma or to turn into a melanoma.

Normal, typical moles are usually small, uniform in color, and symmetrical (the two sides look the same). They have sharp, regular borders, and they are usually located on parts of your body that are exposed to the sun. Most of them first appear sometime between early childhood and age 40, and the moles on a particular person's body all tend to look the same. Moles that fit this description are of no concern.

Moles that should be brought to a doctor's attention include:

- Moles that are present at birth
- Moles that first appear during middle age or later
- Any mole that has changed in appearance
- Any mole that itches or bleeds
- Any mole that shows one of the "ABCD" signs of an atypical mole. Doctors use the ABCD mnemonic to help patients remember some of the differences between atypical moles and typical ones.

The four letters stand for the following:

"A" stands for "Asymmetry." A mole that is not symmetrical (that is, one in which one half doesn't look like the other half) is an atypical mole.

"B" stands for "Border Irregularity." A mole with a ragged or blurred edge or with notches in the edge is atypical.

"C" stands for "Color." A mole that contains a variety of different colors or shades is atypical.

"D" stands for "Diameter." A mole with a diameter larger than that of a pencil eraser is atypical.

All atypical moles - and any other skin changes or irregularities that concern you - should be examined by a doctor. Often, the doctor can tell just by looking (sometimes with the aid of a magnifying device called a dermatoscope) that the unusual-looking area is not skin cancer. In other instances, the doctor may need to perform a biopsy. This is a simple diagnostic test, performed in the doctor's office, in which a sample of the abnormal area is removed and sent to a laboratory to be examined under a microscope.

If you do spot an abnormality on your skin, there's no need to panic. Even if the abnormality turns out to be skin cancer (and it probably won't), it will almost certainly be curable. The important thing is to show the abnormality to a doctor promptly so that if it is skin cancer, it can be treated right away.