Sun and skin – a dangerous combination

Activity 1

Protecting skin from the sun

  1. How do sunscreens work?

  2. How long before going out in the sun should you apply sunscreen?

  3. What protection level of sunscreen should you use?

  4. How often should you reapply your sunscreen?

  5. What does the sun protection factor (SPF) number on a sunscreen mean?

  6. What precautions should be taken with chemical sunscreens?

  7. Are there any potential disadvantages of using chemical sunscreens?

  8. What products other than a chemical sunscreen can you use to protect your skin from the sun?

  9. What is the name of the skin pigment that gives protection from ultraviolet (UV) radiation?

  10. Where is this pigment produced?

  11. What happens during the tanning process?

  12. Do you know of any benefits of small doses of ultraviolet radiaiton?

(Activity used with permission of the NSW Cancer Council.)

Teachers notes

  1. Sunscreens can be either physical or chemical.

    • Physical sunscreens (eg, zinc oxide) form an opaque film over the area where they are applied so that ultraviolet radiation is reflected away from the skin. These preparations are called 'total blocks' because they prevent both UV-A and UV-B from hitting the skin.
    • Chemical sunscreens form a film on the skin which absorbs ultraviolet radiation.
  2. Sunscreens should be applied to clean dry skin at least 15-20 minutes prior to sun exposure.

  3. Authorities now recommend that everyone should use 15+ sunscreen.

  4. Re-apply sunscreen every 2 hours or every hour if you are sweating a lot. Re-apply after swimming.

  5. The sun protection factor numbers range from 4 to 15+ and is a measure based on how long normal, unprotected skin takes to burn when exposed to a dose of artificial sunlight. On average this is about 10 minutes. In theory, if 15+ sunscreen is applied, you are able to stay in the sun for about 150 minutes (15 × 10) before you start to burn. Because the SPF is measured in a laboratory, it is not an accurate guide to the degree of protection a sunscreen will give at different times of day and of the year. A sunscreen of SPF 15 filters approximately 94 per cent of the UV-B rays.

  6. Don't use sunscreens after the use-by date and don't expect them to replace sensible sun avoidance. To avoid any skin allergy or irritation from the sunscreen, do a patch-test on a small area on the arm before applying it to the whole body. Sunscreens are only one component of skin protection and should be used in conjuction with wearing protective clothing and avoiding the midday sun.

  7. A few researchers are opponents of sunscreen use for the following reasons: People using sunscreens tend to stay longer in the sun because they do not get a sunburn – they develop a false sense of security. Most chemical sunscreens absorb UV-B radiation but let most of the UV-A rays through. UV-A rays penetrate deeper into the skin and are strongly absorbed by melanocytes which are involved in sun tanning and melanoma formation. The long-term effects of regular sunscreen application are unknown, but no long-term side effects have been clearly demonstrated.

  8. Loose-fitting long sleeved shirts and long pants of tightly woven fabrics are effective protection. Broad-brimmed or legionnaires hats protect the face and neck from the sun.

  9. Melanin is the dark skin pigment that absorbs UV and is thus a natural sunscreen.

  10. Melanin is produced by melanocytes located in the lower epidermis of the skin.

  11. Melanin production by melanocytes is stimulated by exposure to sunlight. As more melanin is produced, the skin darkens.

  12. About 75 per cent of the body's vitamin D supply is generated by exposure to UV-B rays.
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Posted March 1997.