Physical vs Chemical Sunscreens

This section of the guide explains the differences between physical and chemical sunscreens. There are pros & cons to both.

PHYSICAL SUNSCREENS

Sunscreens that use physical filters as the primary active are called physical sunscreens. Sometimes they are called mineral or inorganic sunscreens.

Physical sunscreens work by absorbing, reflecting, and scattering UV rays from the surface of the skin. These ingredients form a shield over the skin. When UV rays hit the skin, they bounce off this ’shield,’ which inhibits penetration into the skin. In reality, full deflection does not happen. Invariably, some rays will get through.

There are two physical filters used in the industry. Both are made of minerals:

• Zinc Oxide
• Titanium Dioxide

Memorize these. You’ll be looking for these ingredients.

Zinc Oxide and Titanium Dioxide can also be reduced to nano-sized particles (15-100 nm). When they are in nanoparticle form, they absorb UV rays (rather than reflect them).

Both Zinc Oxide and Titanium Dioxide are safe and very stable in formula and when exposed to the sun. They are not absorbed by the skin (unless in nanoparticle form), and therefore do not cause reactions.

They are excellent choices for people with sensitive or reactive skin. In fact, Zinc Oxide is also an anti-irritant and skin protectant, and is commonly used in sensitive skin care lines.

Sunscreens for sensitive skin use one or both of these ingredients.

Particle Size Matters

One major drawback of mineral sunscreens is that they tend to produce a white cast on the skin. This is due to the mineral particles. The more cosmetically elegant formulations have micronized these mineral particles to minimize the white cast.

Micronization means the particle size has been made much smaller, sometimes into nanoparticles (the smallest size). Nanoparticles of Zinc Oxide and Titanium Dioxide leave no white deposit. Formulas with micronized particles tend to be less thick and heavy too.

Micronization comes with a tradeoff though. The more micronized the particles, the thinner the ‘shield’ and the less protected you are. Larger particle sizes protect better (but they make skin appear whiter.)

The other tradeoff is nanoparticle safety, which remains controversial and unclear. The verdict is still out.

Not all formulas containing Zinc Oxide or Titanium Dioxide will give you a ghostly white cast. So don’t eliminate them before trying. More and more sunscreens are offering high percentages of the minerals without the whiteness.

Comedogenicity

Because non-nano mineral sunscreens are occlusive (create a layer over skin that blocks pore openings), they can sometimes be comedogenic and cause breakouts. But don’t assume they are bad for you.

Whether or not you get clogged pores and breakouts is due to a bunch of factors, e.g. skin type, sebum levels, pore size, skin renewal rate, hormones, diet, and much more (see Causes of Acne). It’s usually not one ingredient that is to blame.

You will soon realize that there are few choices for good sunscreen actives in the U.S., so don’t rule these two choices out.

CHEMICAL SUNSCREENS

Sunscreens that use chemical filters as their primary active are called chemical sunscreens. Sometimes they are called organic sunscreens.

The term ‘chemical sunscreen’ is confusing but is used widely in the industry. Technically speaking, everything on this planet is made up of chemicals (except light and electricity). *Everything* is a chemical! So it’s silly to call something a ‘chemical’ sunscreen. Physical sunscreens are made of chemicals too. But this is the common nomenclature in the industry, so we’ll stick with it.

Chemical sunscreens work by absorbing the energy of UV rays and converting it to heat that is dispersed in the skin.

Some of the most common chemical filters are:

• Avobenzone
• Ecamsule (Mexoryl SX is the trade name, exclusive to L’Oreal)
• Octinoxate
• Octisalate
• Octocrylene
• Oxybenzone

Each chemical filter has its pros & cons. Have you ever felt stinging in your eyes after applying sunscreen? That irritation is often caused by a chemical filter. Some chemical filters cause contact and irritant dermatitis and photosensitivity.

Without going into painstaking detail about the pros & cons of each chemical filter, let me just highlight the key point, the one that really matters:

Avobenzone, which is the most common UVA chemical filter you will see, is very unstable and degrades in sunlight.

Stabilizing Avobenzone

Avobenzone can be photo-stabilized by Octocrylene and other photostabilizers, but this can produce irritation. For example, Neutrogena’s patented Helioplex formulation stabilizes Avobenzone by DEHN (an electron acceptor) and Oxybenzone.

New versions of Avobenzone and new delivery technologies, such as liposomes, are starting to address this problem. Avobenzone can be encapsulated into liposomes, which are closed lipid spheres that target delivery of the encapsulated ingredient(s) into specific areas of the skin. To picture a liposome, think of a bubble with liquid inside it, like a Vitamin E capsule.

Unfortunately, you will not necessarily know whether Avobenzone has been stabilized or liposomally encapsulated unless the company makes a point of mentioning it in its marketing copy. The only way to find out for sure is to ask the company directly.