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Though the studies are only in-vitro (made in the lab, not on real people), and it also has a high comedogenicity index, it might be worth a try if you are prone to inflamed acne (the type that's caused by P. acnes bacteria).

Once inside the skin, it hydrates, but not from the outside - putting pure water on the skin (hello long baths!) is drying. 

One more thing: the water used in cosmetics is purified and deionized (it means that almost all of the mineral ions inside it is removed). Like this, the products can stay more stable over time. 

The other reason is that it’s mild and works very well combined with other cleansing agents and surfactants. The art of cleansing is usually to balance between properly cleansing but not over-cleansing and cocamidopropyl betaine is helpful in pulling off this balance right. 

Oh, and one more nice thing: even though it’s synthetic it’s highly biodegradable. 

More info on CAPB on Collins Beaty Pages.

Also, if your skin is sensitive, fragrance is again not your best friend. It’s the number one cause of contact allergy to cosmetics. It’s definitely a smart thing to avoid with sensitive skin (and fragrance of any type - natural is just as allergic as synthetic, if not worse!). 

If you are into chemistry (if not, we understand, just skip this paragraph), the reason is that electrolytes (you know, the Na+ and Cl- ions) screen the electrostatic repulsion between the head groups of ionic surfactants and thus support the formation of long shaped micelles (instead of spherical ones) that entangle like spaghetti, and viola, a gel is formed. However, too much of it causes the phenomenon called "salting out", and the surfactant solution goes runny again. 

Other than that, salt also works as an emulsion stabilizer in water-in-oil emulsions, that is when water droplets are dispersed in the outer oil (or silicone) phase. And last but not least, when salt is right at the first spot of the ingredient list (and is not dissolved), the product is usually a body scrub where salt is the physical exfoliating agent. 

The first main difference is that while TiO2 gives a nice broad spectrum protection, Zinc Oxide has an even nicer and even broader spectrum protection. It protects against UVB, UVA II, and UVA I almost uniformly, and is considered to be the broadest range sunscreen available today. 

It's also highly stable and non-irritating. So much so that Zinc Oxide also counts as a skin protectant and anti-irritant. It's also often used to treat skin irritations such as diaper rash.

As for the disadvantages, Zinc Oxide is also not cosmetically elegant. It leaves a disturbing whitish tint on the skin, although, according to a 2000 research paper by Dr. Pinnell, it's slightly less white than TiO2. Still, it's white and disturbing enough to use Zinc Oxide nanoparticles more and more often. 

We wrote more about nanoparticles and the concerns around them here, but the gist is that if nanoparticles were absorbed into the skin that would be a reason for legitimate health concerns. But luckily, so far research shows that sunscreen nanoparticles are not absorbed but remain on the surface of the skin or in the uppermost (dead) layer of the skin. This seems to be true even if the skin is damaged, for example, sunburnt. 

All in all, if you've found a Zinc Oxide sunscreen that you are happy to use every single day, that's fantastic and we suggest you stick with it. It's definitely one of the best, or probably even the best option out there for sun protection available worldwide. 

Anyway, it doesn't matter if it reflects or absorbs, Titanium Dioxide is a pretty awesome sunscreen agent for two main reasons: it gives a nice broad spectrum coverage and it's highly stable. Its protection is very good between 290 - 350 nm (UVB and UVA II range), and less good at 350-400 nm (UVA I) range. Regular sized Titanium Dioxide also has a great safety profile, it's non-irritating and is pretty much free from any health concerns (like estrogenic effect worries with some chemical filters).

The disadvantage of Titanium Dioxide is that it's not cosmetically elegant, meaning it's a white, "unspreadable" mess. Sunscreens containing Titanium Dioxide are often hard to spread on the skin and they leave a disturbing whitish tint. The cosmetic industry is, of course, really trying to solve this problem and the best solution so far is using nanoparticles. The itsy-bitsy Nano-sized particles improve both spreadability and reduce the whitish tint a lot, but unfortunately, it also introduces new health concerns. 

The main concern with nanoparticles is that they are so tiny that they are absorbed into the skin more than we want them (ideally sunscreen should remain on the surface of the skin). Once absorbed they might form unwanted complexes with proteins and they might promote the formation of evil free radicals. But do not panic, these are concerns under investigation. A 2009 review article about the safety of nanoparticles summarizes this, "to date, in-vivo and in-vitro studies have not demonstrated percutaneous penetration of nanosized particles in titanium dioxide and zinc oxide sunscreens". The English translation is, so far it looks like sunscreens with nanoparticles do stay on the surface of the skin where they should be.  

All in all, Titanium Dioxide is a famous sunscreen agent and for good reason, it gives broad spectrum UV protection (best at UVB and UVA II), it's highly stable, and it has a good safety profile. It's definitely one of the best UV-filter agents we have today, especially in the US where new-generation Tinosorb filters are not (yet) approved.