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Some studies have tested whether the biological effects of UV radiation depend only on the total amount of radiation received during a tanning session, commonly referred to as total dose, independently from the intensity of UV radiation and from exposure time.
For instance, experiments were carried out to see if the effects of UV radiation at equal total dose are the same regardless of whether exposure is
On the one hand, experiments carried out on human and mouse skin show that the sunburn effect (erythema) of UV radiation depends only on the total dose of UV radiation received and not on the intensity or duration of exposure.
On the other hand, experiments in which UV radiation was used to induce cancer in mice show that, for a fixed total dose, the risk of cancer increases when radiation is less intense but lasts longer or when radiation is intermittent instead of continuous. More...
UV radiation covers a broad range of wavelengths and different wavelengths have different effects on the skin. For instance, UVB is much more effective than UVA in causing sunburn. To determine the maximum strength of radiation that is safe, it is necessary to consider not only the amount of radiation for each wavelength but also how effective each wavelength is at producing sunburn.
At present, suggesting safe exposure limits is only appropriate for short-term effects such as sunburn. It is not possible to suggest such limits for long term effects like skin cancer, especially melanoma.
When using a sunbed for cosmetic purposes, the UV radiation dose has to be large enough to produce tanning but not so large that it causes marked or severe sunburn. Experience has shown that the best results are obtained with an exposure approximately at or just below that to induce a just perceptible reddening of the skin 8 to 24 hours after exposure.
Regarding sunburn, the exposure dose that should not be exceeded on any single occasion depends on skin type and ranges from 100-300 J/m2 for highly susceptible skin types I and II to 700 – 1200 J/m2 for skin types V and VI with low susceptibility.
A classification of skin phototypes based on susceptibility to sunburn in sunlight
Since the biological effects of UV radiation depend only on the total amount of radiation received during an exposure session, regardless of whether exposure is to high-intensity radiation for a short period of time or to low-intensity radiation for a long period of time, the prescribed sunbed session should be no less than 10 minutes. This would limit the intensity of the associated radiation to a more moderate level. That way, the risk of sunburn which might result from exceeding the session time limit is minimized and the risk of melanoma hence possibly reduced.
The dose from each session should not be large enough to cause sunburn and the maximum intensity of the radiation used should not exceed 0.3 W/m2. This is equivalent to a UV index (UVI) of 12, which would be typical in summer in Darwin, Australia; and Colombo, Sri Lanka and which WHO describes as “extreme”.
At present, it is not possible to give a safe limit for long-term effects such as the risk of skin cancer, especially melanoma, because there is no threshold dose below which cancer will not occur. Consequently, any recommendation about a limit value of total dose is arbitrary and subjective. Some institutions have set a limit of 20 sessions per year but others have set a limit which is nearly four times as high. Other agencies have simply advised against sunbed use and have not specified an “acceptable” maximum annual usage. More...
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