Many factors determine how much UV you are exposed to, including:
- Time of year
- Time of day
- Weather conditions
UV rays are strongest in areas close to the equator. Because the sun is directly over the equator, UV rays only travel a short distance through the atmosphere to reach these areas. UV radiation is also the strongest near the equator because ozone in these areas is naturally thinner, so there is less to absorb the UV radiation.
UV exposure is lower in areas further from the equator because the sun is farther away. Exposure is also decreased because UV rays must travel a greater distance through ozone-rich portions of the atmosphere to reach the earth’s surface.
UV exposure is also greater in areas of snow, sand, pavement, and water due to the reflective properties of these surfaces.
Altitude is another contributing factor to the amount of UV. Higher altitudes have greater UV exposure because there is less atmosphere to absorb UV rays.
Time of Year
The sun’s angle in relation to the Earth varies according to season. During the summer months the sun is in a more direct angle, resulting in a greater amount of UV radiation.
Time of Day
UV is most intense at noon when the sun is at its highest point in the sky, and UV rays have the least distance to travel through the atmosphere. Especially in the hot summer months, it is a good idea to remain indoors during the peak sun hours of 10am and 4pm.
Many people believe that you cannot get sunburned on a cloudy day; this is simply not the case. Even under cloud cover it is possible to damage your skin and eyes, and cause long-term damage. It is important that you protect yourself with sunscreen, even in cloudy weather.
Some surfaces, such as snow, sand, grass, or water can reflect much of the UV radiation that reaches them. Sunglasses rated for 100% UV protection, a wide-brim hat, and broad-spectrum sunscreen can help protect your eyes and skin from reflected UV rays.