Sun protection factor (SPF) is a number on sunscreen labels that shows how long skin can be in the sun and maintain a low risk for sunburn. The higher the SPF number, the longer it protects a person from the sun's burning rays.
It is important to read the information on the sunscreen label about the SPF factor listed on the label and how much protection it gives the skin. The sunscreen should be applied according to the directions on the label so it is most effective in protecting the skin from the sun's ultraviolet rays.
No sunscreen gives total protection, but "broad-spectrum" sunscreens that contain ingredients such as avobenzone, benzophenones, cinnamates, salicylates, sulisobenzone, titanium dioxide, and zinc oxide usually protect from ultraviolet A and B (UVA and UVB) rays. The label of the sunscreen product will say what types of UV rays it protects the skin from.
Sweating heavily, swimming, or doing other water activities reduces the SPF because sweat or water on the skin will reduce the amount of protection the sunscreen provides. Sunscreen needs to be reapplied more frequently during these activities.
Sun and Medication
Some medicines may cause your skin to sunburn more easily. Medicines used for treatment on the skin (topical) or for the whole body (systemic) can cause two types of reactions:Phototoxicity. Medicines react with proteins in the skin and sunlight and cause a more severe sunburn reaction with increased redness, swelling, pain, and occasionally blistering. This reaction is more localized to the skin and usually does not involve an entire immune system response. UVB light is likely to cause this type of reaction. Photoallergy. Medicines react with skin proteins and ultraviolet light (UV) to create a substance (antigen) in the bloodstream that causes an allergic skin reaction. This type of reaction involves the immune system, and the antigen can remain in the body and cause future skin reactions with exposure to sunlight. UVA light is likely to cause this type of reaction.
Examples of medicines that may cause your skin to sunburn more easily include:Some antibiotics. Aspirin, ibuprofen (such as Advil or Motrin), and naproxen (such as Aleve). Skin products that contain vitamin A or alpha hydroxy acids (AHA). Some acne medicines. Some diabetes medicines that you take by mouth.
If you are taking a medicine, it is important to know if the medicine may cause your skin to sunburn more easily.Prescription medicines usually have instructions that will advise you to stay out of the sun or to wear sunscreen if the medicine can increase your skin's sensitivity to sun exposure. Nonprescription medicines may have precautions to avoid the sun on the label.
Some chemicals in common products can also cause photoallergic reactions. These products include:Whitening agents used in laundry soaps and bleaches. Lotions or perfumes that contain musk. Sunscreens that contain para-aminobenzoic acid (PABA).