How to apply chemical sunscreen

What should the label say?

Chemical sunscreens absorb ultraviolet radiation, also called UV radiation. Broad spectrum means protection against both UVA and UVB rays, while SPF primarily describes protection against UVB, the main cause of sunburn. Check for both broad spectrum coverage and SPF 30 or higher rather than choosing by the SPF number alone. On UK sunscreens, look for at least four stars for UVA protection; a UVA circle indicates that the product meets the EU standard.345

How much should you apply, and where?

1. 1Start before you leave. Allow 15 minutes before sun exposure. For an outing long enough to risk burning, NHS advice is to apply twice: 30 minutes before leaving and again just before going out.
2. 2Measure enough. Most adults need at least about one ounce, roughly a shot glass, to cover skin not covered by clothing. A larger body can need more. For the face, use at least one teaspoon, approximately enough to cover the length of your index and middle fingers.
3. 3Spread the sunscreen thoroughly over exposed skin. Avoid your eyes and mouth. Applying too thinly reduces protection, so do not stretch a small amount across a large area.
4. 4Check the easily missed spots. Include your ears, nose, back of the neck, hands, hairline, tops of the feet and exposed scalp. Ask someone to help cover your back if needed. Use SPF 30 or higher lip balm for your lips.

When should you reapply?

Reapply every two hours while outdoors, and straight after swimming, sweating or towel drying. Reapply when sunscreen has rubbed off, too. Water resistant does not mean waterproof: the label states whether water resistance lasts 40 or 80 minutes during swimming or sweating. Follow the bottle's directions rather than treating water resistance as permission to skip another application. A higher SPF does not give you a fixed number of extra hours in the sun.156

Can you use a spray instead?

Sunscreen comes in lotions, creams, gels and sprays, because even one job apparently needs a product aisle. Sprays help reach areas such as the back and shoulders, but applying too little is a common problem. A lotion or gel is a practical choice when you want more control over coverage. Never spray sunscreen directly onto your face, and avoid inhaling the spray. Read the directions for your particular format.67

Check the bottle before using it

Sunscreen labels carry protection ratings, application directions and expiry information, making the small print unusually qualified for its job. Discard expired sunscreen. For a US sunscreen without an expiry date, discard it three years after purchase; discard it sooner if you do not know its age. Keep the container out of excessive heat and direct sun, using shade or a towel to protect it outdoors.6

What else matters outdoors?

Use sunscreen on cloudy days and in winter, too. No sunscreen protects against every UV ray, so also use shade, covering clothing and a wide brimmed hat. For babies under six months, prioritize keeping them out of direct sunlight and ask a doctor before applying sunscreen. If sunburn makes you feel unwell or causes severe swelling or blisters, seek medical help.1256