Sunscreens 2000 -- What You Need To Know

by

Douglas Barcon, Pharm.D., CEO

Summer is here.  These pages will cover the basics of what you need to know to protect yourself from sunburn while getting a great tan.

Invisible ultraviolet light from the sun is responsible for sunburn.  The infrared heat-generating light from the sun can cause a burn too, but its not a photochemical type reaction as is caused by ultraviolet light.   The human body can sense the heat generated by infrared light, which allows the person to recognize the potential burn early and take protective precautions.  The ultraviolet light that causes sunburn cannot be sensed by the body, and consequently the person doesn’t know they have been burned until it’s too late.  Since the body cannot sense ultraviolet light with a wavelength between 280 nanometers and 400 nanometers (nm), which is the range that causes sunburn, a better term for it is ultraviolet radiation.  Only sunburn due to ultraviolet radiation within this wavelength range will be discussed throughout this section.

Types of Sunburn Ultraviolet Radiation

There are three types of ultraviolet radiation from the sun:

UV-C radiation is less of an issue, since it doesn’t reach the earth’s surface, because it is absorbed by the ozone layer in the atmosphere.  If the ozone continues to thin, however, some of it can penetrate to the surface, so it may eventually become an issue to address.  UV-C is normally generated by man-made devices for its germicidal effect.  Although it is much less damaging than UV-B radiation, caution must be exercised because a sustained exposure can potentially lead to erythema (redness) or sunburn with little if any tanning.   Protection from UV-C radiation should only be necessary when tanning from artificial sources that do not filter UV-C radiation.

UV-A radiation can cause sunburn and premature aging of the skin, but generally less than UV-B radiation, depending on the person’s skin type along with tanning.  Even though UV-A radiation is considered to be weaker and less damaging than UV-B radiation, it can still cause sunburn because there is about 100 times or more of it reaching the Earth’s surface than UV-B radiation.  UV-A radiation is not absorbed by the ozone layer, while a considerable amount of UV-B radiation is absorbed by the ozone layer.  As the ozone layer thins, more UV-B radiation reaches the Earth’s surface to cause an increase in skin cancer.   Generally, the amount of tanning is related to how much UV-A radiation energy is allowed to reach the skin.  Another important property of UV-A radiation is that it is responsible for photosensitivity reactions that occur in people taking certain drugs, like tetracyclines, phenothiazines, and tricyclic antidepressants.

UV-B radiation is the main culprit in sunburn and is quite effective at it, but it can also cause tanning.  It can also cause premature aging of the skin and can potentially lead to skin cancer.  As the wavelength of the UV radiation gets shorter, it carries more photon energy that is dissipated when it strikes the epidermal layers of the skin.  This energy causes sunburn by disrupting the physiology of the skin cells.  UV-B radiation at a wavelength of 300 nm is considerably more damaging to skin than is UV-B radiation at a wavelength of 320 nm, but both cause sunburn to unprotected skin and both can increase the chances of getting skin cancer.  Even though the amount of UV-B reaching the Earth’s surface is one one-hundreth that of UV-A, it takes one one-thousandth the amount of UV-B energy to cause the same minimal erythemal dose as UV-A.  In comparison, UV-C energy only one-fourth that of UV-B radiation can cause the same minimal erythemal dose.

Copyright 2000 Solumedia and Douglas Barcon, Pharm.D.   All rights reserved.  This information may not be published, duplicated, or transmitted in any manner without the express written permission of Solumedia and the author.

Legal Info:  The information provided in Sunscreens 2000 is as is without any warranty or liability.   Although considerable attention has been taken to ensure its accuracy, both the author and Solumedia are not liable for any errors or omissions or for any damage or injury that might occur from the use or improper use of this information.  This information is provided solely as an educational public service.

This page was last updated on 04/29/05.