At first the numbers may seem random, but it is in fact a linear scale. So, if you determine that you are a skin type II and burn in 30 minutes at a UV index of 6, then you will likely burn in 15 minutes at a UV index of 12. 

The UV index is one of the three key factors for managing your sun exposure. You need to know your skin type, which determines your reaction to sun, the UV index, how strong the sun is, and then determine the proper duration to give you a minimal erythemal dose of UV exposure to produce vitamin D and other healthy properties - including nitric oxide - without burning. You just want to get a *smidge* pink the next day.

One of the easiest ways to know the UV index wherever you are is to download the free dminder app on your phone!

Want to understand skin type? Read last week's news.

Cedric F. Garland, Dr., PH, FACE

UC San Diego School of Medicine

Last week there was an article which summarized Richard Weller's position on sunlight - that it is necessary. One of the quotes was that in the UK "deaths from heart disease are a hundred times higher than deaths from skin cancer."

I decided to see if it is true for the US as it is a great statistic to use in our work. Here's what I found using American Cancer Society (ACS) and American Heart Association (AHA) data:

Best wishes,

Cedric

Read Paper 

Dr. Han van der Rhee, et al., conducted an extensive review study based on 71 original studies, 21 meta-analyses, 6 systematic reviews and 17 reviews (115 total), by researchers from the Netherlands representing dermatology, public health, and molecular cell biology. The research team reviewed both the positive and negative effects of sun exposure and concluded that both too much and too little sunlight may be harmful to our health.

Similarly, a systematic review of 26 case-control and 19 cohort studies demonstrated a consistent inverse association between chronic sun exposure and the following cancers: colorectal-, breast-, prostate-, and non-Hodgkin's lymphoma.

A review of epidemiological studies suggest that regular exposure to the sun and a natural exposure to bright light during the day with less light in the evening is inversely associated with the risk of cancers of the colon-, breast-, prostate-, and non-Hodgkin's Lymphoma, as well as multiple sclerosis, and metabolic syndrome (including hypertension and diabetes mellitus).

Review table 7 of the paper for more detail on this list of biological effects of sunlight - effects and implications.

Human skin adapts to regular, non-burning, sun exposure with increased melanin (pigment in the skin),a thickening of the stratum corneum (outermost layer of epidermis), and a reduction in cyclobutane pyrimidine dimers (CPD) a substance known to cause overall cell damage. Research on these effects have found that regular exposure to doses of solar-simulating artificial UV for 3 weeks decreases the ultraviolet sensitivity of the skin for erythema (redness) on average by 75%.

Regular exposure to UV, as experienced by outdoor workers and regular sun bathers, leads to an almost complete disappearance of DNA damage in the basal and suprabasal layers of the epidermis, where skin cancer occurs, because it is in these lower levels of skin where the cells are replicating. In contrast, DNA damage in the top layers of the epidermis doesn't have the same consequences because the cells are already committed to cell death.

The Australian prevention programs of "Slip! Slop! Slap!" (to "slip" on a shirt, "slop" on sunscreen, and "slap" on a hat) and SunSmart established in the 1980s have been adopted and copied by most Western countries. The primary messages of these programs have been avoidance of the mid-day sun, the use of protective clothing, and use of sunscreens with a SPF of 30 or higher that protect against UVA and UVB. Rather than tailor the message to the conditions of individual countries or regions, the same sun exposure advice is used all over the world. While the message is appropriate for persons with sun-sensitive skin living in countries with high ambient UV, such as Australia, it is less applicable in other parts of the world where chronic exposure and outdoor occupations are associated with a relatively low risk of melanoma and basal cell carcinoma and even squamous cell carcinoma.

"Most skin cancers are caused by a mismatch between skin type and geography and/or sun exposure related lifestyle."

"It is obvious that excessive sun exposure and sunburn should be avoided. During sun-seeking vacations an adequate protection is needed. It is, however, unlikely that continuous protection during daily life contributes to our health, particularly in countries with a temperate climate. Both too much and too little sunlight may be harmful to our health."