Ultraviolet radiation exposure and dose explained

UV dose is important

When we go outside on almost any day, no matter how cold or cloudy, we receive some UV exposure from the sun to our hands, face, eyes and any uncovered skin. The intensity of the UV we are exposed to and the time we are exposed for result in a UV dose. If we get too much UV in a short time we can receive a UV dose that is high enough to cause painful sunburn. The UV dose we build up over a long period of time (years) can increase our risk of cancers on our skin and cataracts in our eyes. It's important to find a balance between the small UV dose that we need to be healthy and not getting too much. Our sun exposure habits over many years, especially in childhood, and the resulting UV dose we accumulate increases the chance of us getting skin cancers in later life.

Realtime UV reports and UV dose reports

The Realtime UV reports can show us how intense the UV is at any time of the day but our dose depends on both the UV level and the time we are exposed to it. Our total UV dose builds up over the day and it is this cumulative dose that can lead to sunburn and skin damage. We can use the UV dose reports to estimate when we must take sun protection precautions or risk overexposure.

How much UV exposure is too much?

When we work, play and relax outdoors in the sun it's often difficult to judge how much of a UV dose we are getting. On cool and cloudy days there is still a lot of UV reaching the ground and we often aren't aware of how much there is.

The UV Dose chart shows accumulated UV dose in units of Standard Erythemal Dose or SEDs. A very fair-skinned person can receive sunburn and skin damage from only two SEDs. Be aware that sunburn may not show on the skin for 16 to 24 hours after receiving a high UV dose.

Use the SED chart to estimate your UV dose

The chart shows three things:

  • How much UV dose you could receive for each hour of the day, updated at the end of each hour.
  • The total UV dose for the whole day, updated each hour.
  • The predicted UV dose for a clear sky day.

Further information about SEDs

A SED is a standard measure of UV dose. One SED per day is considered safe for most people. You should consider taking sun protection measures if you could be subjected to a UV dose of more than one SED especially if you have fair skin. People with fairer skin experience skin damage quicker than people with darker skin.

Fitzpatrick Skin Types

The most commonly used scheme to classify a person’s skin type by their response to sun exposure in terms of the degree of burning and tanning was developed by Thomas B. Fitzpatrick, MD, PhD.

PDF iconFitzpatrick skin types chart