Understanding how sunscreens work is key to finding the right sunscreen for your condition. Many sunscreens protect only against UVB light. But the light spectrum has different wavelengths: UVA, UVB, visible, and infrared and more. Depending on your medical condition, you may be sensitive to more than one type of light. For example, some people are sensitive to both UVA and UVB type light. People can be sensitive to UVA, UVB and visible light. Some people are even sensitive to infrared light.
You need to match up a sunscreen with your personal light sensitivity. Try a high SPF sunscreen, but recognize many sunscreens only protect against UVB light. UVB is measured with Sun Protection Factor (SPF) ratings. Try sunscreens that protect against UVA light; UVA protection is measured with a Persistent Pigment Darkening (PPD) rating. The higher the PPD rating, the better amount of UVA protection. Because sunscreen products are regulated under restrictive FDA guides in the U.S., some sunscreens can only be sold in Europe and Canada.
Once you have the sunscreen, you need to apply enough sunscreen and store the sunscreen properly, and discard the sunscreen when it becomes too old. A high SPF sunscreen rating of 50 theoretically protects you 50 times as long in the sun as without the sunscreen. But in real life, the rating is reduced considerably because people often don't apply enough sunscreen. Old or improperly stored products can lose effectiveness and will provide less protection than the rating specified on the container.
Understanding the different types of light/radiation and the relationship to sunscreens
The solar spectrum is composed of different types of radiation. Radiation is energy that travels and spreads out as it goes. There are many different types of radiation: ultraviolet (UV), visible light and infrared (IR) and more. The different types of light/ radiation are defined by wavelength measured in nanometers (nm). The sun is a source of invisible ultraviolet (UV) radiation. It is the UV rays that cause our skin to burn. UV light also causes the heat we all recognize. Ultraviolet light is divided into UVA, UVB and UVC ranges.
UVB measured with SPF: (290-320nm)
Most commercial sunscreens protect against UVB.
UVB sunscreen rating is measured with the Sun Protection Factor (SPF) rating. SPF measures how well a sunscreen protects you against sunburn and UVB light. Theoretically, a sunscreen with an SPF rating of 10 should allow you to stay in the sun ten times longer than without sunscreen.
UVB can burn the skin resulting in sunburn. Everybody is sensitive to UVB.
UVA measured with PPD: (340-400nm)
Sunscreens that protect against both UVA and UVB light are called broad spectrum sunscreens.
UVA sunscreen rating is measured with Persistent Pigment Darkening or PPD rating which measures pigmentation present at 2 hours after the end of exposure to UVA. PPD measures how well a sunscreen protects you against UVA light.
UVA ages the skin.
UVA can cause skin to tan.
UVA is not blocked through glass (like in the car); therefore, people with UVA sensitivity will not be fully protected by glass. Window glass blocks virtually all UVB but only a portion of UVA energy. Glass filters for windows can be purchased to block more of the UVA spectrum.
UVA protection is now offered in many suncreens. Formulations with butyl methoxydibenzoylmethane (avobenzone) provide some protection for mid- to long-range UVA rays. In formulations where avobenzone is not photostable, UVA protection rapidly decreases with the time spent under the sun. A number of different companies have developed systems to stabilize avobenzone in the final formulations and evidence of effectiveness can be determined by the PPD rating. Helioplex is one combination available in Neutrogena products.Formulations combining avobenzone with ecamsule (terephthalylidene dicamphor sulphonic acid [Mexoryl SX™, L´Oréal]) provide another photostable system for UVA protection. These sunscreens include products by Anthelios. Formulations combining avobenzone with dometrizole trisiloxane (Mexoryl XL™) can be found in sunscreens sold under different brands including Anthelios™, Ombrelle™, Vichy™ and Biotherm™ (L'Oréal). Formulations combining avobenzone with bemotrizinol and bisoctrizole (Tinosorb S® and Tinosorb M® respectively, Ciba Specialty Chemicals) are another combination providing protection.
Visible light or blue light: (400-700nm)
Visible or blue light rating - there is no current rating of sunscreens for visible light.
Sunscreens with inorganic ingredients such as iron oxide, titanium dioxide, and zinc oxide provide some protection for visible light.
Infrared light (above 700nm)
There is no current sunscreen rating for infrared light.
Most UVC radiation is absorbed by the ozone in the atmosphere and does not reach us.
There is no current sunscreen rating for UVC
What is your light sensitivity and medical condition?
Depending on your sun sensitivity, you may be sensitive to different wavelengths of light including UVA, UVB and visible light. Think of having a roof over your head with three holes in it- one hole for UVA light, one hole for UVB light, and one hole for visible light, and it is raining. Sunscreens which only protect against UVB light will not completely protect you, and you will get exposed to the UVA and/or visible light. So searching and finding the right sunscreen for your condition can make a huge difference in your light tolerance.
What is your light sensitivity? Most people are sensitive to UVB. If you have problems through windows, then you might be sensitive to UVA. If you are sensitive to indoor lights, then you might be sensitive to the UVB in florescent lighting or visible light. Some people are sensitive to infrared. Each person has a unique personal light sensitivity. One person with light sensitivity might have Solar Urticaria, Polymorphic Light Eruption(PMLE), a reaction to a medication, or another of many conditions. A person with Solar Urticaria may be sensitive to UVB, while another person with Solar Urticaria may be sensitive to UVB and UVA. Again, one person with PMLE may be sensitive to UVB, while another person with PMLE may be sensitive to UVB and UVA. Each person has a unique light reaction profile.
Applying and using Sunscreen
Apply sunscreens to dry skin 20 minutes before going outside. Shake the bottle well and apply thickly and thoroughly.
Be sure to use enough sunscreen. Most people only use half as much as they are supposed to. As a rule of thumb, use one teaspoon to cover the face, neck, and ears; one teaspoon to cover the front; one teaspoon to cover the back of the body; and one teaspoon for each arm or leg not covered with clothing. A typical twist off cap from a soda bottle (or beer bottle) is about one teaspoon. If you only use half as much sunscreen as you should, you are only getting half the protection. [Schneider] Don't forget to put sunscreen on your ears, the base of the neck, the tops of feet, and the backs of knees. One study on photosensitive patients showed they only applied 1/4 of the recommended amount of sunscreen.[Azurdia]
Reapply every 2 hours. Reapply after swimming or sweating. Many sunscreens are very fragile and are easily rubbed off.
Don't store sunscreen in the car and other places where temperatures may get high. Heat may change the chemical composition of sunscreens.
Throw out your old sun block. The chemical composition of sunscreens can change with age, and it may no longer perform as stated on the bottle. Check the expiration date.
Understanding SPF and PPD values of sunscreen ratings
To review, SPF measures how well a sunscreen protects you against sunburn and UVB light. Theoretically, an SPF rating of 10 should allow you to stay in the sun ten times longer than normal. Persistent Pigment Darkening (PPD); measures how well a sunscreen protects you against UVA light. Theoretically, a PPD rating of 10 should allow you to stay out in the sun ten times longer.
People with extreme photosensitivities may have reactions in just a matter of minutes, so we need the highest SPF and PPD ratings possible.
In real life, people rarely get the SPF or PPD protection as the rating on the sunscreen bottle because: not enough sunscreen is put on in the first place, sunscreen is wiped or sweated off, sunscreen is left on too long and is no longer effective, and a variety of other factors limiting effectiveness.
As an example, someone who reacts to the sun in 5 minutes uses an SPF sunscreen of 30. But she only put on a third as much as she should have. Therefore, the SPF rating of 30 is reduced by one third to a value of 10 because she didn't apply enough sunscreen. An SPF of 10 is supposed to increase a person's tolerance time in the sun by a multiple of 10, so 50 minutes could be spent in the sun. In our example, 5 minutes x 10 =50 minutes sun tolerance with sunscreen, because 10 is the SPF rating of the thinly applied sunblock and 5 minutes is the person's sun tolerance without sunscreen.
Theoretically for SPF or PPD values above 30, light protection does not increase significantly. There have been some arguments that there is no need for an SPF rating of greater than 30. Some nation’s regulations only allow sunscreens to have a maximum SPF rating of 50+, and no higher. Some critics argue that it is difficult to test high SPF ratings. But if we consider all of the real life factors, then we must see that all the ratings get reduced by more than half to one fifth of the specified SPF rating. Those of us with extreme sun sensitivity and short sun tolerance time need those extremely high SPF ratings.
Comparative Sunscreen ReviewsBest sunscreens and product safety from the Environmental Working Group (EWG): a list of top-rated sunscreens and makeup. They have several articles under the “sunscreens exposed” section, a “hall of shame” listing those they recommend avoiding, and sun safety tips.
Best rated sunscreens from Consumer Search. The Full Report provides a description of “What To Look For”. http://www.consumersearch.com/sunscreen/review
Makeup Alley for consumer reviews.
Azurdia RM, Pagliaro JA, Diffey BL, Rhodes LE., Sunscreen application by photosensitive patients is inadequate for protection. Br J Dermatol. 1999 Feb;140(2):255-8.
Bissonnette, R., Medscape: Innovaderm Research, Montreal, QC, Canada
Menter JM, Hatch KL., Clothing as solar radiation protection., Curr Probl Dermatol. 2003;31:50-63.
Rosenstein BS, Weinstock MA, Habib R., Transmittance spectra and theoretical sun protection factors for a series of sunscreen-containing sun care products. ,Photodermatol Photoimmunol Photomed. 1999 Apr;15(2):75-80.
Schneider J. The teaspoon rule of applying sunscreen. Arch Dermatol.2002; 138: 838- 839.
United States Environmental Protection Agency, Sunscreen: The burning facts. EPA 430-F-06-013, September 2006.
Consult with your physician regarding any treatments or medical advice suggested by this website.
We are not physicians, we are people trying to learn about our conditions and better our lives. We try to be accurate, but the articles and advice may have errors, become out-of-date, or even give bad advice.
We highly recommend that you try anything new in moderation, to test for any reaction you might have to the ingredients used.
Copyright 2006-2105 sun1 Support Group for Sun Sensitive People