You should wear sunscreen on skin not covered by clothing everyday you go outside. This is because the sun emits harmful UV rays everyday, rain or shine (up to 80% of harmful UV rays penetrate through clouds!).
Sun protection factor (SPF) is a measure of how much solar energy is required to sunburn protected versus unprotected skin. A higher SPF value indicates a higher protection rating.
When choosing a sunscreen, it is recommended to choose one that offers the following:
- SPF 30 or higher
- Broad spectrum protection
- Water resistance
Not protecting your skin from the UV rays can worsen skin conditions and even lead to developing skin cancer.
Sources:
[1] ‘What does SPF in Sunscreen really mean?’, Office for Science and Society. Available: https://www.mcgill.ca/oss/article/you-asked-general-science/what-does-spf-sunscreen-really-mean.
[2] C. for D. E. and Research, ‘Sun Protection Factor (SPF)’, FDA, Nov. 2018, Available: https://www.fda.gov/about-fda/center-drug-evaluation-and-research-cder/sun-protection-factor-spf.
[3] ‘Sunscreen FAQs’. Available: https://www.aad.org/media/stats-sunscreen.