Glossary

Water Resistance (SPF)

Written by Reviewed by the SYNC editorial team Published Last reviewed Editorial standards

Water Resistance (SPF) — a measured claim describing how long a sunscreen maintains its stated SPF while the skin is wet from swimming or sweating, expressed as either 40 or 80 minutes. It does not mean a product is waterproof, since all sunscreens degrade with water and time and require reapplication.

Key points

  • Regulators permit only two water-resistance ratings on labels: 40 minutes or 80 minutes.
  • The terms waterproof and sweatproof are not allowed because no sunscreen fully resists water indefinitely.
  • Water resistance is verified by testing SPF after the specified time of water immersion.
  • Reapplication after swimming, towel drying, or heavy sweating is necessary regardless of the rating.

Frequently asked

Does water-resistant mean I don't need to reapply?

No, water resistance only lasts for the rated 40 or 80 minutes in water, after which you should reapply, especially following towel drying.

Is any sunscreen truly waterproof?

No product is waterproof, which is why regulators require the term water-resistant along with a specific time rating instead.

Related topics

This is a foundational entry in the SYNC Skin Encyclopedia and is expanded over time. Educational information only — not medical advice.

Encyclopedia

Further reading

This entry was written and checked against the sources below. They are published by clinical and scientific bodies, they are listed most readable first, and each one opens in a new tab. They are background for the whole entry rather than footnotes to individual sentences.

  1. How to select a sunscreen American Academy of Dermatology Clinical guidance aad.org
  2. Sunscreen FAQs American Academy of Dermatology Clinical guidance aad.org
  3. How to decode a sunscreen label American Academy of Dermatology Clinical guidance aad.org
  4. Sunscreens and Photoprotection StatPearls (NCBI Bookshelf) Reference text ncbi.nlm.nih.gov
  5. Sun Protection Factor (SPF) U.S. FDA Regulatory and safety fda.gov
  6. Sunscreen: How to Help Protect Your Skin from the Sun U.S. FDA Regulatory and safety fda.gov

SYNC does not publish medical advice. Nothing here replaces a consultation with a doctor or a pharmacist about your own skin.