Differences between Chemical Sunscreen and Physical Sunblock

I have got this question many times: what is the difference between a sunscreen and a sunblock? I've also found that many people have some misunderstandings about physical sunblock, dreading it as something you have to apply a lot, which will in turn become cakey and leave a white cast. One reader even told me that it seems like a product of the last century. :) So I've decided to take it upon myself to debunk those myths by answering some questions, and then do a comparison between the two types of sunscreens. 

Question 1: How much sunscreen/sunblock do you have to apply?

Answer: For chemical sunscreens, you have to apply at least a third of a teaspoon in order to have a degree of protection. Many dermatologists also suggest their clients to at least apply 1/2 teaspoon or 1 teaspoon to cover their entire face and neck. 

For physical sunblock, it depends on the product. Yes, in the 1990s, there have been some sunblocks that actually require you to use 1 tablespoon for sufficient protection. However, the Laneige sunblock and most other modern physical sunblocks only requires you to use a pea sized amount to cover your face (not including your neck), so that you actually apply less than chemical sunscreen. Why? Modern formulas have found a way to press the zinc and titanium dioxide closer together so that they are more densely packed. So a modern pea sized sunblock actually contain as much zinc and titanium dioxide as a tablespoon of sunblock made in the 1980s.

Question 2: How do those two products work?

Answer: Chemical Sunscreen work by absorbing the UVA and UVB sunrays so that they do not touch your skin. You have to reapply frequently because the sunscreen can only absorb a certain amount of rays before it becomes void.

Physical Sunblock work by reflecting the UVA and UVB rays so that they cannot touch your skin. The reflecting properties of sunblock wear off eventually so you have to reapply.

Question 3: Which one is better for sensitive skin?

Answer: I find that I and many others react better to physical sunblock, because it does not have an excessive amount of chemicals in them (hence the name). zinc and titanium dioxide are minerals that some people say are good for your skin. Chemical sunscreens usually contain ingredients like avobenzone, which is not bad for your skin either, but most people are more likely to be allergic to avobenzone than to zinc and titanium dioxide. 

In addition, chemical sunscreen has to be absorbed into your skin before it can work (hence wait 15 minutes after application before running out), while physical sunblock lies on top of your skin, so that people with sensitive skins are more likely to be allergic to chemical sunscreen.

Lastly, if you apply sunscreen immediately after moisturizer before it fully absorbs, it might react to some ingredients in your moisturizer, causing allergies. 

Question 4: Which product will give me a better appearance, i.e. not being oily and shiny and not leaving a white cast?

Answer: This question is tricky because both products can be made to be almost invisible after application, so it really depends on the product you purchase. For example, I've used chemical sunscreens that disappears after 5 minute of application, giving me no white cast or oiliness, but I have also used ones that makes me oil up within an hour of use. It is the same with physical sunblock, so it really depends on the product you purchase.

Question 5: Which product is more convenient?

Answer: I would say sunblock for three reasons:

A. I can run out the door as soon as I finish applying sunblock, whereas I have to wait 30 minutes to be safe with sunscreen.

B. Sunscreen must be applied on your skin before any makeup item, or even before your moisturizer if it does not absorb fully and leaves a residue. This is because sunscreen has to be absorbed into your skin before it can work, and having anything on before you apply it can hinder its absorption. 

For this very reason, reapplication is tricky because you have to wash off mostly anything you have on your face.

C. Scientists have recently found that the sun will do more damage to your skin if you applied chemical sunscreen and did not reapply than if you did not apply sunscreen/sunblock at all. (Don't ask me why :))