Sun and the UV Index, Explained Without the Jargon
Sun and the UV Index: what it is, why it matters, and what published guidance actually asks of you.
UV exposure is the main preventable cause of skin cancer, and UV can be strong even on cool or cloudy days.
Key takeaways
- Low: 0 to 2
- Moderate: 3 to 5
- Most useful single change: Check the UV Index in your weather app or on the EPA's UV Index forecast.
- Commonest mistake: Tanning beds and sunlamps.
- See a doctor if any of the signs under "When to speak to a doctor" below apply to you.
The short answer
The daily forecast of ultraviolet radiation strength, and how to use it to plan sun protection.
Where it fits
This is part of Environmental Health. The published position is set out below, along with what it means day to day.
The numbers, in one place
| Measure | Figure |
|---|---|
| Low | 0 to 2 |
| Moderate | 3 to 5 |
| High | 6 to 7 |
| Very high | 8 to 10 |
| Extreme | 11 or higher |
| Sunscreen | broad-spectrum, SPF 30 or higher, reapplied every 2 hours and after swimming or sweating |
What that means in practice
What that looks like in practice:
- Check the UV Index in your weather app or on the EPA's UV Index forecast
- Seek shade, especially between 10 a.m. and 4 p.m.
- Wear a wide-brimmed hat, UV-blocking sunglasses and clothing that covers the arms and legs
- Use about 1 ounce of sunscreen, roughly a shot glass, to cover an adult's exposed skin
- Keep babies under 6 months out of direct sun
What gets people into trouble
Where people most often come unstuck:
- Tanning beds and sunlamps
- Skipping sun protection on cloudy days or in winter near snow, which reflects UV
- Relying on a single morning application of sunscreen
Related topics
- Sun Protection: What the Evidence Actually Says (Skin Health)
- Skin Cancer: What Published Guidance Supports (Cancer Awareness)
- Sun and Heat Abroad: What the Evidence Actually Says (Travel Health)
- What the Guidance Really Says About Vitamin D and Bone (Bone and Joint)
Where to go next
- What People Get Wrong About Sun and the UV Index
- New to Sun and the UV Index? Start Here
- Sun and the UV Index — the reference entry
- Environmental Health: The Complete Guide
- Household Chemicals: What the Evidence Actually Says
- Lead in Homes and Water: Sorting the Evidence From the Noise
When to speak to a doctor
See your doctor or a dermatologist for a new or changing mole, a sore that does not heal, or blistering sunburn in a baby. Call 911 for heat stroke signs such as confusion, fainting, a body temperature of 103°F (39.4°C) or higher, or hot, red skin with a fast pulse.
Where this comes from
- EPA — UV Index Scale
- American Academy of Dermatology — How to Prevent Skin Cancer
- FDA — Sun Protection Tips: How to Help Protect Your Skin
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.
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