Reapplying sunscreen is important for your sun protection. Fact. Reapplying sunscreen maintains sun protection. Fact. However, it is a myth and wrong that it allows you to stay in the sun for an unlimited length of time.

Honestly, it is not that easy to write about the length of time spent in the sun and reapplying sunscreen. With regard to the length of time spent in the sun, there is a practical and a theoretical perspective. In other words, there is the “play it safe” view and the “maximum possible” view. However, variables play a role in both viewpoints. Not straightforward, right? 

But we want to address the topics surrounding our beloved sun and the all-important sun protection in a clear and, above all, easy-to-understand way for everyone. For that reason, the topic of reapplying sunscreen is important and necessary. It’s very simple.

Difference between theory and practice 

Since 1975, the different skin types have been categorized on a scale that is still used today. Knowing your skin type can help you to better plan the necessary protective measures. Here is a little example that only relates to the theory: Assume you have skin type 2. After approximately 10 minutes, you see the first signs of redness, and you are using sunscreen with an SPF of 20. That makes 10 minutes x 20 SPF = 200 minutes in the sun. Please note that this value corresponds to laboratory conditions. The spectrum in the laboratory varies from the natural solar spectrum. The SPF measured in the lab is higher than the SPF outside in the real sun. 

This 200 minute value is therefore the absolute “maximum possible”, which should be considered purely theoretical. Because here we come to the variables just mentioned, which can quickly shorten the time span: 

• Not enough sunscreen is used 
• Sunscreen is applied unevenly over the body 
• Mechanical removal, e.g., by clothing or drying with a towel 
• Swimming + sweating 
• The SPF is measured in the laboratory. The light spectrum varies from the natural solar spectrum.

Psychology also plays a role. When you use a sunscreen with a high level of protection, it is easy to believe that you can enjoy the sun with almost no limits or you can even get a little slack with applying the sunscreen. This is a misconception.

To illustrate this point: Using sunscreen does not mean that your skin is 100% protected from UV rays. With SPF 30, for example, approximately 3.3% of UV light ends up on and under the skin and causes damage there. This is associated with chemical reactions and biological processes that are fundamental to our lives, but also involve dangers. 

Skin remembers years later 

While exposed to the sun, the body collects UV rays and thereby fills up its so-called UV account. The amount of “captured” radiation and its effect on skin and eyes accumulates over the course of the day. When the account is full, the first visible signs of skin change will appear, and this is followed by the first visible change, sunburn. Tanned skin is also a reflection of the damage that has occurred and is therefore a false and dangerous beauty ideal.

However, the skin is already affected before sunburn sets in. The damage may not be immediately visible, but it triggers processes that inevitably lead to damage later on. Our skin absorbs all this damage and “remembers” it. Years later, effects such as skin aging and skin cancer can become acute. 

If your skin has been exposed to too much UV radiation throughout the day, you can't reverse this by applying just as much sunscreen. The best things to do is get out of the sun and replenish. If this is not possible, you should still continue to apply sunscreen with a high SPF to avoid even more damage. 

Extending is relative 

But let’s take another look at the need to reapply sunscreen. We have our own protection time and a sun protection factor, e.g., 15. This gives us our maximum time in the sun. After half of this time has passed, some of the UV radiation has already penetrated the skin. However, it is not yet enough to cause sunburn. Even so, it is no longer possible for us to double the protection by reapplying sunscreen. However, reapplying is important simply because sunscreen is lost due to perspiration or water, for example. 

If we theorize, and the variables did not exist, then reapplying the same SPF 15 would mean that your sun protection would double to 30 after half the time. As a result, you would reach your sunburn threshold, your limit of exposure to the sun, even later.

However, reapplying sunscreen may theoretically extend the sun exposure time, but it will never be doubled or even extended for as long as you wish. And in practice, it will definitely not be possible to determine a precise time. Indeed, we do not live under laboratory conditions. Consider the variables.

We therefore recommend that you always choose the “play it safe” option. Your skin and health will thank you. That is for sure. Easy, right?