By Alain Menard, Microbiologist, co-founder of The Green Beaver Company

Natural sunscreens are simple. They contain the minerals zinc oxide and/or titanium dioxide to create a physical barrier on your skin which block and reflect harmful UVA and UVB rays.

Chemical sunscreens, on the other hand, contain a combination of several chemical filters to absorb and convert UV rays into heat. In order to work, a typical chemical sunscreen requires a cocktail of three to five different types of potentially dangerous chemical filters, such as avobenzone, homosalate, octisalate, octocrylene and oxybenzone. Not only do they contain these chemical filters, they contain a lot of them. In fact, many conventional chemical sunscreens contain over 20 per cent pure chemical filters.

1. They can irritate the skin. Some chemical filters are known to cause contact dermatitis in certain people, resulting in red rashes, itchy skin, blisters and red bumps.

2. They can penetrate your skin and circulate in your body. Studies have shown that many chemical filters can penetrate the skin to some degree. Once they do, they can enter your blood stream. So it's not surprising that chemical sunscreens have been found in human blood, urine and breast milk. A US study detected oxybenzone in over 96 per cent of the more than 2,500 children and adults tested.  

3. Some chemical sunscreens are suspected hormone disruptors. Laboratory studies indicate that some chemical sunscreens may mimic human hormones. Hormone disruptors can cause birth defects, abnormal development of growing children and can contribute to the development of cancer. Preliminary studies suggest a link between high concentrations of oxybenzone in the body and an increase risk of endometriosis and lower birth weight in girls.

4. It's bad for the environment. Common chemical sunscreens were shown to kill or bleach coral even at low concentrations.

5. Many chemical sunscreens also contain other unwanted chemicals. Not only may they contain over 20 per cent chemical filters, they may also contain artificial fragrances, chemical preservatives and synthetic polymers. Other common chemicals found in sunscreens that you may want to avoid include acrylates/octylacrylamide copolymer, butane, diethylhexyl 2, 6 naphthalate, dimethicone, methylparaben, PEGs, phenoxyethanol and triethanolamine.

“Make sure you do your homework and read the label of any product claiming to be 100 per cent natural.”

You can avoid chemical filters by choosing a sunscreen with the natural minerals zinc oxide and/or titanium dioxide. But you need to be careful. Just because a sunscreen contains these minerals doesn't guarantee it's 100 per cent natural. Many sunscreens that claim to be "natural" still contain some potentially harmful chemicals.

To be truly natural, the minerals zinc oxide and/or titanium dioxide in the product must not be coated with chemicals like silicone or be micronized to nanoparticles. The base formulation also must not contain other chemicals such as artificial fragrances or chemical preservatives. Instead, a natural sunscreen will have additional non-chemical ingredients that are beneficial for your skin.

To ensure a natural sunscreen is truly what it claims to be, it must be certified by a reputable, independent third-party certifier. This guarantees that the product is authentic. So make sure you do your homework and read the label of any product claiming to be 100 per cent natural.