the dangers of tanning
by Michael Caswell, Ph.D.
It seems to be a never-ending cycle. The public hears from the media of the dangers of tanning; they hear from the dermatologists of the dangers of tanning; and, we hear from the sunscreen companies of the dangers of tanning. What are those dangers and how much danger is there? As a tanning salon operator, it is your duty to familiarize yourself with the important points associated with tanning so you can provide your customers with pertinent, up-to-date information and guide them through the maze of tanning information.
Tanning and Skin Cancer
Exposure to ultraviolet (UV) radiation and the development of skin cancer have been associated for many years, although the mechanisms are not well understood.
There are three basic types of skin cancer--squamous cell carcinoma (SCC), basal cell carcinoma (BCC) and malignant melanoma (MM). MM results in approximately 9,000 deaths per year, while SCC and BCC rarely cause death. Indeed, the incidence of death due to SCC and to BCC is not recorded nationally.
The basis for sunscreens to claim that they prevent skin cancer was made on data generated with albino mice and on human epidemiological data. The epidemiological data showed that as latitude increased, skin cancer decreased. It also showed that outdoor workers have a greater incidence of SCC and BCC than indoor workers. This association of greater incidence of skin cancer with increased UV exposure holds for SCC and partially for BCC, but not for MM. Increased exposure to UV may provide a protective effect against MM.
Additional research suggests that the incidence of BCC decreases after about 35,000 hours of sun exposure. In animal studies, it is well known that albino mice rarely (less than one percent) express BCC as a result of exposure to UV radiation, almost exclusively expressing SCC. However, humans express predominately BCC rather than SCC. This suggests that albino animals are inappropriate models for UV-induced cancer in humans. The reason for this may be genetic. Some new genetically engineered mice may allow scientists to examine how and why BCC is generated.
Tanning and Malignant Melanoma
The difficulty in developing a reasonable mammalian model system to study MM may directly be related to the lack of reciprocity between UV radiation and MM. Non-mammalian systems have been developed, and one of those, a fish model, develops MM in response to simple white light; no UV radiation is required. Clearly, this is not an acceptable model for MM. The lack of a good model system forces the scientific community to examine epidemiological data for the answers to MM.
In addition, the data gathered after many years of research generally proves that total hours of UV exposure is not a significant risk factor for MM.
- The majority of studies on the incidence of MM find that outdoor workers have a lower incidence of MM than indoor workers. This suggests that modest exposure to UV radiation--as would be experienced by an outdoor worker and by the patron of a tanning salon--would be beneficial in protecting against MM. This also suggests that five to 10 years from now, regular patrons of tanning salons may exhibit less MM than a control group, a group that did not use tanning salons.
- Reciprocity in the dose-response relationship does not hold for UV radiation and melanoma. That is the scientist's way of saying that the same dose will not result in the same biological response. Several scientific studies have shown that one or more severe sunburns increases the risk of MM. So, severe sunburns increase your chances of MM.
However, the amount of UV radiation one receives is not a risk factor for MM. In other words, people who receive a lot of UV exposure during their lifetime do not increase their chances of MM--they decrease their risk. This suggests that modest tanning will help protect against MM, because the subject with a tan is less likely to suffer a severe burn as a result of exposure to UV radiation. As we all know, skin exposed to UV radiation will accommodate to the exposures by tanning.
Again, these research publications suggest that a tan produces a significant protective effect against malignant melanoma. Other factors such as nevi incidence, diet, socio-economic class, or Fitzpatrick skin type also may be important in the development of MM.
Tanning and Photoaging
Photoaging, apart from skin cancer, is not a disease; it is a condition. According to scientists, wrinkled skin is observed in the face and neck following many years of overexposure to UV radiation. Wrinkled skin does not seem to occur anywhere but the face and neck. It does not occur on the arms or legs. In addition, other environmental insults to the skin, such as smoking, may contribute to wrinkled skin. Scientists need to conduct more research in this area.
Tanning and Immunology
UV exposure inhibits the ability of the skin's allergy cells to function in the sequence of allergy events. This is often used as therapy in reducing the severity of a poison ivy or a poison oak rash, or in reducing the effects of atopic dermatitis as well as in reducing the effects of psoriasis. Many patrons of tanning salons simply tan to reduce the incidence of their mild to moderate psoriasis, atopic dermatitis, or other immunologically mediated skin disease. This relieves the medical community from a significant burden and allows the patient to achieve some modest relief at a greatly reduced cost. Additionally, some dermatologists recommend tanning salons to their patients.
Excessive exposure of skin to UV radiation can result in UV-induced immune suppression. However, the importance of immune suppression in the incidence of skin cancer is circumstantial at present. Immune suppressed transplant patients clearly show increased incidence of skin cancers, while immune suppressed AIDS patients exhibit no increase in skin cancers. The amount of UV radiation necessary for the development of UV-induced immunosuppression, 5 to 10 MED, is far greater than one would achieve in a tanning bed. To my knowledge, no one has measured the effect of a session in a tanning bed on the immune suppression of the skin. While therapy can be achieved in a tanning bed, the extent and importance of the UV-induced immune suppression in the development of skin cancer is unknown.
Perspective
While most believe that chronic excessive exposure to UV radiation will result in increased risk of SCC, the same may not be true of BCC. Your risk to BCC may decrease after a certain amount of UV exposure.
MM appears to be very different from SCC and BCC. Most scientific data support the ability of modest UV exposure to reduce the risk of MM. My perspective, based on available data, is that scientists may well find that those who tan modestly will exhibit less MM.
