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The Truth About SPF and Sunscreen: How Long Should You Wait Before Reaplying and More

Updated on December 20, 2015
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I'm a dad, husband, and Christian first. The rest is just life's add-ons: an educator, administrator, learning & development professional.


Learn important information about SPF and sunscreen to protect yourself better.

Chances are you've seen labels on sunscreens bottles highlighting the letters SPF followed by a number. Sun Protection Factor or SPF is a measure of how effective a sunscreen product is. Consumers often think the SPF is associated with the time of exposure to UV radiation. They think that an SPF 30 will give them 30 times longer protection before getting sunburn. Unfortunately this is not accurate. It’s not the length of exposure but the amount of radiation that it can protect you from getting sunburn. Simply put, the higher the SPF rating, the more radiation it can repel.

Putting on sunscreen entails more than just slapping on cream on your body. You need to know how to maximize it so you won’t get sunburn. Here are some factors you should consider:

Skin type

The skin type of the person is a huge factor as some people have more sensitive skin than others. Some may absorb sunscreen better while others do not. If the skin does not absorb the sunscreen effectively, it can simply be washed or wiped away easily leaving you vulnerable to sunburn. Moreover, the amount of sweating can also affect the performance of the product. The more you sweat the easier you lose the protection. Your skin type will determine how often you should apply and how long you should wait before going out into the sun after application.

The amount used

The amount used is another important factor in the efficacy of the sunscreen. According to FDA dosage, the average adult must put on 2 mg/cm2. This translates to roughly around 1 oz. of sunscreen for the body and approximately 1/3 teaspoon for the face. Studies have shown that most consumers only use ¼ of what is recommended. As such, one has the adjust the sun protection factor to ¼ of the actual value.

The time reapplication

A recent research by the University of California showed that reapplying sunscreen within 2 hours will be most beneficial. However consumers can reapply more frequently as necessary. In addition, it is best to wait several minutes for your skin to absorb the sunscreen prior to exposure to sunlight. A 15- minute wait is good enough for maximum absorption.

Activity while wearing the sun screen

What you do also affects how long your sunscreen can protect you. Swimming and sweating a lot will drastically reduce your sunscreen’s efficacy thus reapplication must be done more frequently. Even higher SPF sunscreen can not protect you if it is washed off the skin.

Sunscreen ingredients and SPF varies from one product to another. As such, understanding the product and the concept SPF is important so you remain protected. Suffice to say, the best sunscreen is the one that is used properly.


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    • jpcmc profile image

      JP Carlos 5 years ago from Quezon CIty, Phlippines

      Hello akrk,

      I read the articles and they do provide valuable information. The bottom line is that reapplying sun screen is integral in skin health care. Whatever SPF you are using, it is important to follow the instructions to get the most out of it.

    • profile image

      akrk 5 years ago


      i would like to say that it's a nice article, but i found the SPF interpretation in this article differing from the articles i read already.

      i have found these two articles regarding sun protection,the one in the British journal of medicine* saying SPF as "how much longer skin covered with sunscreen takes to burn compared with unprotected skin". the world health organisation mentions it in this PDF** as follows "Topical sunscreens act by absorbing, scattering or reflecting UV. The sun protection factor (SPF) gives an

      indication of the effectiveness of the sunscreens. For example, a sunscreen with SPF 4 means that the UV

      exposure received after spending a given time in the sun is one-quarter that received in the absence of any





    • jpcmc profile image

      JP Carlos 6 years ago from Quezon CIty, Phlippines

      Thanks for the vote up. More than just the length of time under the sun, it's more about the amount of UV that gets to your skin. Unfortunately the atmosphere is unable to block much of it especially during 10AM to around 4PM. Sunscreens simply block off the harmful UV-A and UV-B and while allowing all the healthy Sunny goodness through. :)

    • SallyTX profile image

      Sally Branche 6 years ago from Only In Texas!

      Good info! Voted up & useful!

      I think sunscreen is great for when you plan to be outside in the sun for an extended period, but I personally disagree with the idea we should go around covered with it all the time. We need some exposure to the sun. There hasn't been enough research yet into what the long term effects of completely blocking it's rays every day for an extended period of time will do to a person.

      I think sunscreen is a good thing to use for days on the beach or lake or working out in the yard, but for other times, a sun hat, parasol, or shade tree should do just fine.

    • jpcmc profile image

      JP Carlos 6 years ago from Quezon CIty, Phlippines

      Thanks larry1987. I got sunburn from a recent vacation so I wrote this hub and several others. I hope it can be useful for you and for other hubbers.

    • larry1987 profile image

      larry1987 6 years ago

      really useful..thanks for sharing

    • profile image

      raeye 6 years ago

      very informational and timely. :)

    • jpcmc profile image

      JP Carlos 6 years ago from Quezon CIty, Phlippines

      I have a sunburn right now that's why i wrote several hubs on it. I researched some info and to my surprise that what I new was not right. I just wanted to share info. Thanks for dropping by.

    • Joyce F profile image

      Joyce F 6 years ago from USA

      Nice SPF sunscreen hub. I always wondered how much to use.