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14

All sunscreens are physical barriers, designed to absorb or reflect UV radiation. They rub off over time, and they will rub off faster when exposed to water/moisture, most commonly from sweating or swimming. Friction (e.g. from towel-drying) also removes sunscreen. Some chemical sunscreens do break down when exposed to sunlight and require the addition of ...


10

As it is stated in this Wikipedia article, the sun protection factor (SPF) roughly describes how the time that your skin is able to protect itself from sunburn is elongated. To take the Wikipedia example: if a person develops a sunburn in 10 minutes when not wearing a sunblock, the same person will prevent sunburn for 150 minutes if he/she wears a ...


9

I'd like to add to the existing answer that while sunscreen effectiveness does decrease as it is absorbed into the body, wears off, or is washed off, high SPF sunscreens will still block most sun after the two hours. The FDA recommendations for reapplication every two hours are basically to provide maximum protection, because the level of protection does ...


8

You will want to look for a sun cream that is designed for swimming - don't bother looking for specific ingredients, look for the bottles that say they are for sun and swim. Usually in addition to the SPF they will have a rating or guide as to how often you need to reapply (eg every swim, or every two swims) @ShemSeger's comment is the recommended way to ...


6

These are generally known as glacier glasses. They are rated as Category 4 on the CE scale and you aren't supposed to drive while wearing them. Sunglasses in Category 4 only transmit 4-8% of available visible light. Hidalogos sunglass guide has a very complete list of the different factors in choosing sunglasses. Category 4 come in a wider range of ...


6

According to this health-related website, you should still wear a shirt: You should not think of sunscreen as an alternative to avoiding the sun or covering up. It is used in addition. Sunscreens should not be used to allow you to remain in the sun for longer - use them only to give yourself greater protection. No sunscreen is 100% effective and so it ...


4

Assuming you're reapplying the screen often (sweat washes it away) and it's a quality one, then it would do for what matters sun protection (although you should still properly cover your head with a hat or a bandana or whatever). That being said, I would use a shirt anyways; to protect your skin from the abrasion of the rucksack, to absorb some sweat, and ...


2

If you are a person who burns readily then sunblock at all times plus long sleeve shirt and hat are your only answer. However the danger of sun, IMHO is overrated, compared to the other hazards of life. At one point I used the World Almanac for figures: Fatal skin cancers kill about 2 people per hundred thousand per year. So skin cancer has about the ...


2

As Paul says, think of sunscreen as in addition to other protection methods. So while you can go without a shirt, it's ideal to also wear a shirt and use other protection methods like a hat. As for whether clothing is always better, that in large part depends on the clothing. Some clothing provides good sun protection while others (think shirts with ...


2

I'm going to assume that you are employing the SODIS method of water sterilization. To sum up the details of the process, this method is where you fill plastic pop bottles, (PET), up with rather clear water 3/4 full, shake them up, and let them sit in the bright sun for 5+ hours. The mechanism this works by is by utilizing the UV radiation in sunlight. ...



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