Is Your SPF Really Enough? How Much Sunscreen to Use
The number on the bottle assumes a generous layer. Most of us apply far less — and get far less protection than we think.
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Key takeaways
- SPF is measured with a thick layer of 2 mg per square centimetre — much more than most people use.
- Use roughly half a teaspoon for the face and neck, and about two tablespoons for the whole body.
- Choose broad-spectrum protection (UVA and UVB) with SPF 30 or higher.
- Reapply every two hours outdoors and after swimming, sweating or towelling.
You bought a good SPF 50. You put it on every morning. So why does your skin still seem to tan, burn or develop new pigment? Very often, the answer is the amount.
Why the number on the bottle can mislead
Sun protection factor is tested in a laboratory with sunscreen applied at 2 mg per square centimetre of skin. Research summarised by the British Association of Dermatologists shows that people typically apply between a quarter and a half of that amount — which means the real-world protection can be a fraction of what the label promises.1
How much to use
- Face and neck: roughly half a teaspoon. Some dermatologists suggest squeezing two lines along the length of your index and middle fingers as a visual guide.
- Whole body: around two tablespoons for an adult, according to NHS advice.2
- Do not forget: ears, the back of the neck, the hairline, the tops of feet and the backs of hands — common spots for sun damage on mature skin.
If that feels like a lot, apply in two thinner layers, letting the first sink in for a minute.
What to look for on the label
Choose a broad-spectrum sunscreen that protects against both UVB (the main cause of burning) and UVA (which penetrates deeper and contributes heavily to skin ageing). Dermatology bodies recommend SPF 30 or higher.3 In the UK, a UVA star rating of four or five, or the letters UVA in a circle, signals good UVA protection.2
Reapplying
Sunscreen rubs, sweats and washes off. When you are outdoors, reapply at least every two hours, and straight after swimming, heavy sweating or towelling — even if the product is water-resistant.3 On a normal office day, a morning application on the face may be enough, but top up before a lunchtime walk or a school run in strong sun.
Sunscreen is not a ticket to stay in the sun longer. It works best alongside shade, hats and covering up.
Does makeup with SPF count?
It helps, but you would need to wear an unrealistically thick layer of foundation or powder to reach the labelled protection. Use a dedicated sunscreen as your base and treat SPF in makeup as a bonus.
Sources
- British Association of Dermatologists. Sunscreen fact sheet. bad.org.uk.
- NHS. Sunscreen and sun safety. nhs.uk.
- American Academy of Dermatology. How to apply sunscreen. aad.org.