Sunscreens are very helpful for preventing sun damage and reducing the risk of skin cancers. But there are so many skin-protection products available now, it can be confusing as to what to use.
What is SPF and what does it measure?
SPF is short for “sun protection factor." It is an attempt to measure how long a sunscreen will protect you from sun exposure, particularly the ultraviolet B (UVB) rays. UVB rays cause sunburn and damage the outer layers of skin (epidermis), contributing to the most common forms of skin cancer and sun-related skin damage (actinic keratosis).
The other type of skin-damaging sun rays is the UVA ray that penetrates through the outer layers of skin to the dermal layer where new skin cells are forming. UVA rays can damage the new cell formation and the skin collagen and elastic tissues. It is damage to these tissues that give people with lots of sun exposure that leathery, aged look.
This is also the area where skin tans. The skin cells darken (tan) to protect the skin from sunlight injury, but this also damages the under layer of skin. While a tan is considered a healthy look by some, it damages skin DNA and can trigger cell mutations that lead to melanoma, the worst of the skin cancers. Sunscreens do not block UVA rays unless they are broad spectrum and contain compounds like zinc oxide that block most sun-ray penetration.
What level SPF do you need for the best protection?
If you are out for a very short time - 30 to 60 minutes - and away from peak sun - 10 am to 4 pm - an SPF 15 will probably help reduce sunburn. For longer exposures, a broad-spectrum sunscreen that protects against both UVB and UVA rays will be more effective for prevention of sun damage.
The percentage of UVB that is blocked rises with the SPF number from 93 at SPF 15 to 98 percent at SPF 50. Beyond SFP 50 there is little change, and there are no sunscreens that block 100 percent of UVB or UVA.
What else can help?
But clothing and a running hat can make a difference. There are now plenty of running fabrics with SPF ratings that do a good job of protecting you when you're out in the sun.
Some sun exposure - about 30 minutes - is good as it generates vitamin D, which is an essential component in bone formation. In the UK we don't have year-round sun intensity that will generate vitamin D, so supplements are generally recommended. It is also important to protect your eyes with good sunglasses to reduce the risk of cataracts.
Sun protection should start at birth and continue throughout life. Too much exposure can age your skin and shorten your life if the sun damage leads to melanoma.