CHEMICAL VS PHYSICAL SUNSCREEN.

There are two types of sunscreens available on market: Chemical and Physical.
What is the difference between them, what are the pros and cons to both?
 
Chemical Sunscreens use chemical filters as their primary active ingredient. Chemical sunscreens work by absorbing the energy of UV rays and converting it to heat that is dispersed in the skin. American Academy of Dermatology says: ”Chemical sunscreens work like a sponge, absorbing the sun’s rays”. Some of the most common chemical filters are:
Avobenzone
Ecamsule (Mexoryl SX)
Octinoxate
Octisalate
Octocrylene
Oxybenzone

Pros

• More common, and easy to find in most convenient stores.
• Compare to Mineral, Chemical sunscreens could be invisible and look translucent on the skin. 
  

Cons

• They are occlusive - it means that they create e a layer over skin that blocks pore openings. After application you can feel the film on your skin, or you can tell that your skin can not breathe. It makes physical sunscreens a poor option for oily or combination skin, prone to break-outs and acne. 
  
• Ingredients in chemical sunscreens often cause irritation. They are well known eye irritants, and some chemical filters cause contact dermatitis. Avobenzone, is the most common UVA chemical filter you will see, is very unstable and degrades in sunlight. It can be photo-stabilized by Octocrylene and others, but this can cause more irritation.
• For people with hyperpigmentation (a.k.a sunspots, melisma, chloasma) heat converted from energy of UV rays may worsen this skin condition. 
  

Physical sunscreens use physical filters as the primary active ingredients. They form a shield over the skin, and work by reflecting, and scattering UV rays from the surface of the skin. UV rays bounce off this “shield”, which inhibits penetration into the skin.
They also called mineral or inorganic sunscreens. Because they are made of minerals. There are two physical filters used in the US industry:
Zinc Oxide
Titanium Dioxide
 
Pros

• Both Zinc Oxide and Titanium Dioxide are safe and very stable in formula.
• They are not absorbed by the skin, and therefore do not cause reactions.
  
• They are excellent choices for people with sensitive skin, and commonly used in sensitive skincare lines.
• Zinc Oxide is also skin protectant and has antiseptic properties, and therefore suits for acne-prone and oily skin. 

Cons

• One major drawback of mineral sunscreens is they tend to leave a white cast on the skin, due to the mineral particles.
• Sunscreens with micronized zinc oxide and titanium oxide are more cosmetically elegant formulations and do not leave white shadows on face, also tend to be less thick and heavy. But unfortunately, the more micronized the particles, the thinner the “shield” and less protection it gives. Also formulas with micronized particles are more comedogenic, and clog pores. 
• Physical or Mineral Sunscreens are the best choice that suits to acne-prone, sensitive, oily or combination skin. If you will look on the market you will soon realize there are few choices for good sunscreen available in the US. So memorize them, you’ll be looking for these ingredients.

 
References:

1. American Academy of Dermatology www.aad.org