Does Chlorine Break Down Sunscreen?

It is widely known that applying sunscreen is an important part of protecting your skin from sun damage. But what happens when you jump into the pool right after slathering on sunscreen? Recent research suggests that certain ingredients in sunscreen can react with chlorine found in pools, posing possible negative effects on our health.

Chlorine and Benzophenone-Type UV Filters

Chlorine is commonly used to disinfect pool water and is essential to the water treatment process. Many sunscreens contain benzophenone-type ultraviolet filters, including one of the most commonly used UV filter called avobenzone. When chlorine and benzophenone-type ultraviolet filters come together, potentially toxic transformation-products (TP) can form.^[1]

Transformation Products

Analysis of several benzophenone transformation-pathways has shown that chlorine exposure in water added along with exposure to UV radiation produce many TP’s.^[2] According to toxicity experiments, the formation of these transformation-products can lead to greater toxicity than the original sunscreen benzophenones before they were transformed by exposure to the chlorine.^[3]

Enhanced Toxicity

Enhanced toxicity was observed for almost all the TPs of the studied BPs, suggesting the formation of TPs are more toxic than the original parent compounds during the chlorination process. Although the toxicities of the majority of these products remain unknown, certain products such as substituted chlorinated phenols and acetophenones are known to be toxic and can possibly disrupt thyroid function.^[4,5]

What Does This Mean for Avobenzone or Benzophenone Based Sunscreens?

Both benzophenone-type and avobenzone based sunscreen ingredients may degrade more easily in the presence of both UV radiation and in water that is chlorinated.^[4] In the case of avobenzone, the longer the UV exposure along with chlorine, the higher the levels of breakdown products.^[4]

Important considerations

The research shows that there are several practical considerations when using benzophenone-type or avobenzone based sunscreens:

• Chlorine is typically found in many swimming pools and they may speed up the breakdown of the avobenzone and benzophenone-type ingredients
• Your skin may not be as well protected when using avobenzone and benzophenone based sunscreens if you are using them on a sunny day while in a swimming pool.
• The formation of breakdown product increases the possibility of local irritation to the skin as the sunscreen ingredients break down. However, there is no actual evidence that avobenzone or benzophenone that breaks down in chlorine can actually cause skin irritation.

Conclusion

Results indicate that extensive usage of BP containing products may cause both environmental and human health issues. UV irradiation causes the formation of many different transformational products when exposed to sunscreens used by humans, such as avobenzone.^[2]

Whether these products may cause skin effects and which of them contribute to allergic skin irritations and other possible health effects are still unknown. Toxicity assessments for individual TPs, especially for those having more toxicity, need to be further researched.

Practical tips

Overall, it is very important to reapply sunscreen after going into a swimming pool. This advice may be even more important when using sunscreens that contain avobenzone or benzophenone. Please follow these important practical tips for sunscreen use when going swimming:

Tip 1: “Twice is Nice.” Start by applying two immediately consecutive layers of sunscreen so that you have a thicker layer on before you are exposed to any sunlight

Tip 2: “Reapply Often” It is important to reapply the sunscreen everytime you get out of the water. 

Tip 3: “Find the Shade” Staying out of intense sunlight is very important and can prevent sunburns.

Tip 4: “Sun Protective Clothing” Sun protective clothing is a must when outdoors in the pool. The use of UV rated clothing is recommended.