SPF itself or ‘Sun Protection Factor’ we know as being the main source of defence, but a product claiming it contains SPF does not necessarily make it a good product for protection. According to skincancer.org, the SPF can be judged as a percentage: SPF15 filters out approximately 93 percent of all incoming UVB rays; SPF30 97 percent; and SPF50 98 percent. While those percentage differences seem small, they make a big difference if you are fair or burn easily.
SPF In Make-Up Isn’t Enough
Generally speaking, no one uses enough moisturiser or foundation to get effective protection from the sun, so you should always wear a separate sunscreen under your make-up. Secondly, SPF is only a marker of protection from UVB light from the sun; UVA rays can also be damaging, and broad-spectrum sunscreens offer protection against this where as moisturisers and make-up may not.