Do I really need to reapply my sunscreen?

By now, we’ve already established that it’s important to use sunscreen or at least a moisturizer containing SPF on a daily basis. However, another question that begs asking is, do we need to reapply every two to three hours as often instructed? In the past, I was under the impression that we have to reapply. However, I now understand that this depends on the type of sunscreen you apply, as well as your lifestyle.

Chemical sunscreen
If you’re using a chemical sunscreen that contains active ingredients like Octinoxate, Avobenzone, Oxybenzone, Octoctrylene or Mexoryl just to name a few, then it is necessary to reapply as they absorb the sun’s light energy and convert it safely into thermal energy on top of the skin, which is then released. In simple terms, chemical filters intercept that radiation and transform it into something much less dangerous. The problem is this photochemical reaction uses up sunscreen according to Dr Ellen Marmur in her book Simple Skin Beauty.

Imagine that each chemical sunscreen molecule gets zapped and disappears the second it gets hit by a photon and converts to heat. Rather than wearing off, it is actually used up, like gasoline used by a car or food consumed by your body. That’s why it must be reapplied. The more sun you are getting, the faster sunscreen is used up or breaks down.

Reapply often when you’re out in the hot sun for long periods
So if you’re using a chemical sunscreen and spend a lot of time under the sun, then it’s important to reapply as often as every two hours even though some chemical filters like Mexoryl are said to be active for as long as eight to ten hours. I use such a chemical sunscreen when I head to the beach or pool and I reapply like *ahem* every half an hour. If it’s just a oouple of minutes of casual sun exposure, or if your chemical sunscreen comes with a physical sun blocker ingredient like Zinc Oxide or Titanium Dioxide, then it may not be necessary to reapply especially if you aren’t able to. But your best bet, to ensure that your sunscreen does not get used up quickly on a daily basis, is to use added protection gear like a brolly, a hat or a pair of sunglasses (or all of these).

Physical sunblock
On the other hand, if you use a mineral sunscreen or physical sunblock as they’re known containing either Zinc Oxide, Titanium Dioxide or both, then you don’t have to reapply as these physical blockers sit on the skin and provides a shield against the UV rays – unless you do not apply enough or you wipe them off due to perspiration. That also means that if you use a sunscreen containing Zinc Oxide and/or Titanium Dioxide only, then you definitely have to reapply when you go swimming.

My recommended type of sunscreen for outdoor usage
But do note that in terms of protection level, a chemical sunscreen combining chemical filters like Mexoryl with physical blockers like Zinc Oxide or Titanium Dioxide offers a higher level of protection – like those from the European brands such as La Roche-Posay that state their PPD ratings. So I would highly recommend using those if your skin is predisposed to pigmentation and you have to be exposed to the oppressive heat for longer periods. In another post, I’ll discuss how to up the ante of sun protection from within our body.

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