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11

The exact value depends on a lot of things - skin tone, the time of day, latitude, how deep the shade is,... The study Vitamin D effective ultraviolet wavelengths due to scattering in shade found that the UVB radiation at 280–320 nanometers that is needed for vitamin D production dropped to levels at around 50% in a tree shade and under an umbrella. It ...


7

About 1/4 - it varies with the reflectivity of the surface, and angle of the sun. Detailed study is at http://www.ncbi.nlm.nih.gov/pubmed/20199222


5

In short: UV bulbs for reptiles and tanning beds emit mainly UV-A, which does not promote vitamin D synthesis but can promote skin cancer. UV light and vitamin D synthesis (Skin Cancer Foundation): Our bodies manufacture vitamin D when the sun's ultraviolet B (UVB) rays interact with 7-dehydrocholesterol (7-DHC) present in the skin. However, we can ...


3

As critiqued in comments, this answer possibly misrepresents the vitamin D situation, which is better described here. Proceed with suspicion! Summary Because of the associated cancer risk, protecting your skin from sunlight is a good idea, also when swimming, and especially by wearing UV-absorptive clothing. Sunscreen makes a huge difference too. You can ...


3

I like your curiosity and logical thinking - you're just missing a few pieces of the puzzle. The sun emits ultraviolet light radiation which is the component of sunlight that is able to damage skin. Ultraviolet (UV) is a form of electromagnetic radiation with wavelengths between 10 to 400 nanometers, shorter than that of visible light but longer than X-rays. ...


2

I don’t know if they can be used, but they shouldn’t. Recently, sun exposure is considered more and more harmful to the skin. This is why for recommended Vitamin D levels, no sun exposure whatsoever is usually assumed, and only intake via diet considered. Because ultraviolet rays from the sun and tanning beds can cause skin cancer, the American Academy of ...


1

This may not be the exact issue alluded to in your source, as it’s not caused by the shape of the mask directly, but Fisher, Williams, & Shaffer (2010) finds that the effectiveness of UV germicidal irradiation is limited by the accumulation of soil (skin residue) on N95 FFR masks, which decreases the penetration of UVGI. See: https://www.cdc.gov/niosh/...


1

There are many possibilities here, but my first thought upon seeing the pictures and reading that it occurred after you increased your alcohol consumption was rosacea. It can be triggered by alcohol consumption. Certain foods can trigger it as well. You'll want to google "rosacea" and "rosacea triggers" because there's much more info out there than I can ...


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