Ask the Expert: Skin Cancer

Dr. Walter K. Nahm, MD, PhD, a Sharp-affiliated dermatologist, answers frequently asked questions about skin cancer.

How is skin cancer detected?
Melanoma skin cancers are detected by applying the ABCD rule to a mole.

  • Does the mole have Asymmetry (meaning one side of the mole looks different from the other side)?
  • Is the Border of the mole jagged and uneven?
  • Are there multiples Colors in the mole (blue, red, black, pink, brown)?
  • Finally, is the Diameter of the mole greater than 5 millimeters or greater than the size of a pencil eraser head?

If you find a mole with these characteristics, contact your physician to set up an exam and obtain a professional diagnosis.

How can skin cancer be prevented?
There are several ways to help prevent a skin cancer. Avoidance of peak ultraviolet rays during the middle of the day, the use of a wide-brimmed hat and sunscreen usage are the staples to prevention. Sunscreens that contain titanium or zinc oxide, Parsol 1789 and Mexoryl are broad-spectrum agents that will offer the most protection. Generally speaking, these sunscreens should be used every two hours during sun exposure and more frequently after toweling, sweating or when water sports are involved.

Can I use the sunscreen I bought last summer or do I need to purchase a new bottle each year?
Unless indicated by an expiration date, the FDA requires all sunscreens be stable at their original strength for at least three years. While you can use the sunscreen you bought last summer, keep in mind that if you are using the appropriate amount, a bottle of sunscreen should not last very long. Approximately 1 ounce of sunscreen — enough to fill a shot glass — is considered the amount need to cover the exposed areas of the body properly.

Does SPF 30 have twice as much sun protection as SPF 15?
UVB protection does not actually increase proportionately with a designated SPF number. For example, an SPF of 30 screens 97 percent of UVB rays, while an SPF of 15 screens 93 percent of UVB rays and an SPF of 2 screens 50 percent of UVB rays. However, inadequate application of sunscreen may result in a lower SPF than the product contains.

Whatever sunscreen SPF is chosen, wearing sunscreen should not provide a false sense of security about protection from UVB exposure as no sunscreen can provide 100 percent UVB protection. While using a higher SPF provides greater UVB protection than a lower SPF, it does not mean that you should stay out in the sun longer.

Find a San Diego Oncologist
To find a Sharp-affiliated doctor, search for a San Diego oncologist or call 1-800-82-SHARP (1-800-827-4277), Monday through Friday, 8 am to 6 pm.