Sunscreen, also known as sunblock and suntan lotion, is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet (UV) radiation and thus helps protect against sunburn. Diligent use of sunscreen can also slow or temporarily prevent the development of wrinkles, moles and sagging skin.
Sunscreen use can help prevent melanoma and squamous cell carcinoma, two types of skin cancer.
A 2013 study concluded that the diligent, everyday application of sunscreen can slow or temporarily prevent the development of wrinkles and sagging skin.[9] The study involved 900 white people in Australia and required some of them to apply a broad-spectrum sunscreen every day for four and a half years. It found that people who did so had noticeably more resilient and smoother skin than those assigned to continue their usual practices
It is important to note that sunscreens with higher SPF do not last or remain effective on the skin any longer than lower SPF and must be continually reapplied as directed, usually every two hours.
Different sunscreen ingredients have different effectiveness against UVA and UVB.
(https://en.wikipedia.org/wiki/Sunscreen)
Not wearing sun protection can cause serious damage, like sunburn, heatstroke, dehydration and even skin cancer.
SPF:
Sun cream is rated with an Sun Protection Factor number. SPF refers to how long that sun cream will keep you protected. So, if you generally burn after half an hour when you’re in the sun a bottle of SPF 30 sun cream will keep you protected for 30 times that length (15 hours). You still need to reapply sun cream often though, especially if you’ve taken a dip in the water or have dried yourself with a towel. Children need really high SPF sun cream, as their skin is much more sensitive to the sun than adults.
(http://www.boots.com/toiletries/suncare)
The sun emits two types of ultraviolet rays that are damaging to the skin. UVA and UVB rays both cause different types of damage, and not all sun creams protect against them in the same way, so it’s important to know the difference between the two, and what they’re responsible for.
UVA rays:
These are present at all times during daylight hours, and while you might not immediately see their effects, they’re very powerful – they can penetrate clouds and even glass. They penetrate the skin more deeply than UVB to cause long-term damage (including all types of skin cancer) and play a major part in the ageing process, such as causing wrinkles, sun spots and leathery skin.
UVB rays:
These are the rays that are mostly responsible for sunburn and skin reddening. They don’t penetrate as deeply as UVA rays, but they’re just as damaging. They play a large part in the development of skin cancers including melanoma.
UVA Star Ratings:
Many forms of sun protection carry a UVA star rating on the bottle - Boots developed this rating system in 1992, and it was Europe’s first measurement system for UVA protection. Ranging from 0 to 5, this rating indicates the percentage of UVA radiation that’s absorbed by that particular sun protection, compared to UVB. The higher the star rating, the better the protection against UVA rays. The lowest recommended star rating for UVA protection is 4.
(http://www.boots.com/sun-and-holiday-inspiration/spf-factors-uva-and-uvb)
Broad Spectrum:
Broad-spectrum sunscreens protect the skin from both UVA and UVB rays. Beginning in December 2012, the U.S. Food and Drug Administration (FDA) began to implement new rules for "broad-spectrum" products.
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