One important rule when wearing sunscreen is to reapply it after two hours. This is said to provide lasting protection from UV rays, reducing your risk of sunburn, skin damage, and other associated consequences. But why is it after every two hours and not longer? Does reapplication really maximize the effectiveness of your sunscreen?

Two-Hour Sunscreen Reapplication: Why is it Necessary?

Continue reading as we explain further the reasons behind the two-hour reapplication rule and the factors that affect sunscreen efficacy. 

Sun exposure breaks down the active ingredients

The active ingredients in the sunscreen provide sun protection by absorbing or blocking UV light. These ingredients, which account for about 10 to 30% of what’s in your sunscreen, filter the sun and commonly fall into one of two categories: physical or mineral) and chemical (or organic).

  • Mineral/physical sunscreens – create a physical barrier to reflect UV rays, so they don’t get absorbed into the skin. Common ingredients in physical formulas include titanium dioxide and zinc oxide.
  • Organic/chemical sunscreens – absorb the UV light, convert it into heat, and then release it from the skin. Chemical ingredients include oxybenzone, avobenzone, octinoxate, and octisalate.

Exposure to UV rays, however, can cause them to slowly break down and become less effective as they perform their job. This is also the reason why it is recommended to store your sunscreen away from direct light and heat. Failure to do so can cause the active ingredients in the product to break down and make your sunscreen ineffective.

For further reading: 9 Ways to Up Your Sunscreen and Sun Protection Game

Sunscreen can rub off your skin  

Similar to your makeup, sunscreen application doesn’t last throughout the day. Some of the product can easily transfer to your fingers (especially if you like to touch your face) and rub off on the clothes you wear and the chair/bench you sit on, as well as towels and sand. This is why you need to reapply it even if you haven’t been in the water

If you’re mostly in a shaded area, the sun may not fully break down the ingredients in your sunscreen, but many of the things you do can cause the products to rub off your skin and other things. Not reapplying can then increase your susceptibility to sun damage.   

Take note: Your face (particularly the eye area) is more sensitive than other areas of the body. This means that it may require a sunscreen specifically designed for the face or sensitive skin. Face sunscreens have lighter consistency like Dr. Sylvia’s Sunshield SPF 45. This is lightweight, non-greasy, and suitable for sensitive skin. 

Sweat and water can wash away sunscreen

Activities such as swimming, exercising, and playing sports can wash or rub away sunscreen. Water can remove the SPF from the surface of the skin and therefore reduce the effectiveness of the formula. Sweating profusely has the same effect and can expose your skin to the effects of UV light.

But what about broad-spectrum sunscreens that are labeled waterproof or water-resistant? Should they be reapplied every two hours too? Yes, you should still reapply them, especially every time you dry off with a towel. No sunscreen, furthermore, is 100% waterproof. This is why experts recommend reapplying sun protection after getting in the water. 

Higher SPF doesn’t mean better protection

SPF or sun protection factor refers to the relative measure of how long the UV rays would take to burn (or redden) your skin compared to the amount of time without sunscreen. You can multiply this length of time by the SPF number on your sunscreen, which is said to determine how the sun protection will last.  

If your skin, for instance, burns after 20 minutes and you’re using SPF 30 (30 x 20 = 600 minutes), does this mean that you could stay in the sun for 10 hours? Not really. This calculation works mostly in theory, as scientists measure SPF using a lamp or artificial source that constantly emits UV light.

In reality, however, UV rays can be very intense and damaging during certain hours of the day. It is still possible for your skin to burn faster if you’re in the sun, especially during peak hours. And sunscreen, as previously mentioned, can easily be rubbed off by clothes, towels, water, and sweat. 

Sun protection beyond sunscreen

A broad-spectrum sunscreen, especially when applied the right way, offers good protection from the sun. It should not, however, be the only form of sun defense you can rely on. Other sun protection measures include:

  • Seeking shade or using an umbrella
  • Covering up with protective clothing
  • Accessorizing with wide-brimmed hats and UV-blocking sunglasses
  • Avoiding exposure during sun’s peak hours (between 10 am and 3 pm)

Several factors can reduce the protective properties of the sunscreen, which makes reapplication necessary. Reapplying every two hours helps make sure that your skin stays adequately protected.

For further reading: Less Effective Sunscreen? Stop Doing These Things When Applying SPF

For more skincare tips and product recommendations, browse through our blog. You can also contact Cutis Medical Laser Clinics in Singapore to learn more about our aesthetic services and schedule a consultation with our aesthetic doctor.