What SPF sunscreen should I use, and how often should I reapply?

I only remember sunscreen on beach days, and I usually grab whatever bottle is cheapest. My sister says I need SPF 50 every day, my friend says SPF 15 is plenty. Does the SPF number matter much, what does 'broad spectrum' mean, and how often do I really need to reapply?

Concerns & risks

You use sunscreen inconsistently, you're unsure which SPF to buy, and you don't know how often to reapply when you're outdoors.

At a glance: reapply moments
Moment	Reapply?
Two hours outdoors	Yes
After swimming	Yes, per water resistance time
After towel drying	Yes
Cloudy day outside	Still yes; UV passes through clouds

FDA photo of a baby in a sun hat under a beach umbrella (FDA official image), annotated: Under 6 months: shade first, says FDA — Under 6 months: shade first, says FDA. Image: FDA (official source, cropped and annotated by ReportSpeed)

Overview diagram: Sunscreen basics — Broad spectrum SPF 15+; Apply generously; Reapply every 2 hours; Add shade and hat — The whole fix at a glance: broad spectrum spf 15+, apply generously, reapply every 2 hours, add shade and hat. Original diagram by ReportSpeed

Causes & evidence

SPF measures protection against UVB rays, the main cause of sunburn. 'Broad spectrum' means the product passed FDA testing for protection against UVA rays too, which contribute to skin ageing and skin cancer. The FDA says sunscreens with a broad spectrum label and SPF 15 or higher help reduce the risk of skin cancer and early skin ageing when used as directed with other sun protection. The FDA advises reapplying at least every two hours, and more often after swimming or sweating, following the label's water resistance time of 40 or 80 minutes. For infants under 6 months, the FDA recommends keeping them out of the sun rather than using sunscreen.

UV exposure is strongest around midday, and reflective surfaces like water, sand and snow can increase it. The FDA tests sunscreen claims such as broad spectrum and water resistance.

Troubleshooting flowchart: try each step in order and stop when it is fixed — What SPF sunscreen should I use, and how often should I reapply — Work through it in order and stop when the problem is gone. Original diagram by ReportSpeed

Applying once in the morning and assuming you're covered all day is how most sunburns happen.

What to do

Step illustration: numbered steps for What SPF sunscreen should I use, and how often should I reapply — The steps from this answer as numbered cards. Original diagram by ReportSpeed

Comparison chart: Sunscreen label basics at a glance (FDA) — Sunscreen label basics at a glance (FDA). Original diagram by ReportSpeed

Sunscreen label basics at a glance (FDA)
Label item	What it means
SPF	Protection against UVB (sunburn)
Broad spectrum	Also tested for UVA protection
SPF 15+ broad spectrum	FDA says it helps reduce skin cancer risk when used as directed
Water resistant (40 or 80 min)	Reapply after that time in water or sweat
Reapply	At least every 2 hours

Choose a product labelled broad spectrum with SPF 15 or higher; many people prefer 30+.
Apply generously to all exposed skin about 15 minutes before going out.
Reapply at least every two hours and right after swimming or towel drying.
Add shade, a hat and sunglasses during peak sun hours.
Keep babies under 6 months out of direct sun and ask a paediatrician about sunscreen.

Common mistakes:

Using too little product
Forgetting ears, neck and the tops of feet
Using expired sunscreen

ReportSpeedMan tip: Check the expiration date; the FDA requires one unless stability testing shows the product lasts three years, and old sunscreen may not work as labelled.

What I would actually do

a broad spectrum SPF 30 I like enough to wear daily, a phone reminder every two hours outdoors, and a hat in the car.

The trade-off people miss: a higher SPF used thinly can protect less than a lower SPF used generously.

How to know it worked

You finish a day outdoors without sunburn and reapplying has become automatic.

Quick FAQ

Is SPF 100 twice as good as 50?
No; protection rises only slightly at higher SPFs.

Do I need sunscreen on cloudy days?
Yes, UV passes through clouds.

Is sunscreen safe for babies?
FDA advises keeping infants under 6 months out of the sun.

Wrap-up: Use broad spectrum SPF 15 or higher, apply generously and reapply every two hours. Pair it with shade and a hat for the best protection.

Wiki: Dehydration.

What SPF sunscreen should I use, and how often should I reapply: read the originals

Step-by-step photos

1. Before The problem
2. Why it happens The cause
3. The fix The fix
4. After The result

⚡ Speed Summary

Use broad spectrum SPF 15 or higher, apply generously and reapply every two hours.
Check the expiration date; the FDA requires one unless stability testing shows the product lasts three years, and old sunscreen may not work as labelled.
Applying once in the morning and assuming you're covered all day is how most sunburns happen.

What SPF sunscreen should I use, and how often should I reapply?

Concerns & risks

Causes & evidence