UV Index

UV Index — a standardized scale that forecasts the strength of ultraviolet radiation from the sun at a given place and time, typically running from 0 upward. It helps people gauge daily sun exposure risk and plan protective measures, with higher numbers signaling a greater potential for skin damage.

Key points

• The UV Index is an international scale, developed with guidance from the World Health Organization, that estimates UV radiation strength.
• Values are generally grouped as low (0-2), moderate (3-5), high (6-7), very high (8-10), and extreme (11 and above).
• UV Index levels are influenced by factors such as time of day, season, latitude, altitude, cloud cover, and reflective surfaces.
• Sun protection like sunscreen, shade, and protective clothing is typically recommended when the index reaches 3 or higher.

Frequently asked

At what UV Index should I wear sunscreen?

Sun protection is commonly advised when the UV Index is 3 or above, though many people apply daily sunscreen regardless because UV exposure accumulates over time.

Can the UV Index be high on a cloudy day?

Yes, clouds do not block all UV radiation, so meaningful exposure can still occur on overcast days, especially when the forecast index is high.

Related topics

• What Is a Humectant?
• What Is the Skin Barrier?

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