What does SPF 50 mean?

How long does SPF 50 last?

SPF measures a dose of radiation, not a length of time. Sunlight is more intense around midday than early morning or late evening, so the same UV exposure can accumulate much faster. Location and cloud cover also affect the intensity. Your skin type, the amount you apply and how often you reapply affect protection too. Sunscreen wears off, and swimming, sweating and friction can remove it. SPF 50 therefore cannot tell you how long you can stay outside without burning.1

Does SPF 50 protect against UVA?

Check for UVA protection separately rather than choosing by the SPF number alone. Ultraviolet A rays, or UVA, contribute to early skin aging and skin cancer. Broad spectrum sunscreen protects against both UVA and UVB. In the US, that wording means the sunscreen has passed a test showing UVA protection proportional to its UVB protection. A sunscreen label has several separate jobs, even if the SPF number gets the starring role.3

On UK labels, look for at least four stars for UVA protection alongside SPF 30 or higher. The letters UVA inside a circle indicate that the sunscreen meets the EU standard for UVA protection.4

Should you choose SPF 30 or SPF 50?

Choose at least SPF 30 with broad spectrum protection. SPF 30 filters about 97% of UVB rays, while SPF 15 filters about 93%. SPF 50 provides greater sunburn protection than SPF 30, but no sunscreen filters out all UVB rays. For extended time outdoors, choose broad spectrum SPF 50 or higher. Higher SPF does not replace shade, protective clothing, a hat or sunglasses.256

Also look for water resistance, especially for swimming or sweating. Water resistance lasts either 40 or 80 minutes, depending on the label; it is separate from SPF. No sunscreen is waterproof.35

How to get the protection on the label

Applying sunscreen too thinly reduces its protection. An SPF number can describe the sunscreen, but it cannot do the applying for you.4

1. 1Apply generously and evenly to exposed skin, including your face, neck and ears. Adults covering the entire body should use around six to eight teaspoons.
2. 2For an outing long enough to risk burning, apply sunscreen 30 minutes before leaving and again just before going out.
3. 3Reapply every two hours outdoors. SPF 50 does not extend that interval.
4. 4Reapply straight after swimming, towel drying, sweating or rubbing sunscreen off. Follow the product's water resistance and reapplication directions.

Who needs extra care?

Take extra care if you burn easily, have many moles or have a family history of skin cancer. All skin tones need sun protection. For sensitive skin, mineral sunscreen containing zinc oxide or titanium dioxide is an option dermatologists recommend. Keep babies under six months out of direct sunlight. If sunburn causes severe swelling, blisters or feeling unwell, seek medical help.24