Oxybenzone This penetration enhancer (i.e., chemical that helps other chemicals penetrate the skin) undergoes a chemical reaction when exposed to UV rays. When oxybenzone is absorbed by your skin, it can cause an eczema-like allergic reaction that can spread beyond the exposed area and last long after you're out of the sun. Experts also suspect that oxybenzone disrupts hormones (i.e., mimics, blocks, and alters hormone levels) which can throw off your endocrine system. According to the Centers for Disease Control and Prevention (CDC), 97 percent of Americans have this chemical circulating in our bodies, as it can accumulate more quickly than our bodies can get rid of it.
Octinoxate One of the most common ingredients found in sunscreens with SPF, octinoxate is readily absorbed by our skin and helps other ingredients to be absorbed more readily. While allergic reactions from octinoxate aren't common, hormone disruption is: the chemical's effects on estrogen can be harmful for humans and wildlife, too, should they come into contact with the chemical once it gets into water. Though SPF products are designed to protect skin from sun-induced aging, octinoxate may actually be a culprit for premature aging, as it produces menacing free radicals that can damage skin and cells.
Retinyl Palmitate (Vitamin A Palmitate) Just like the vitamin A we eat, retinyl palmitate is an antioxidant. As an ingredient in sunscreen, it's function is to improve the product's performance against the aging effects of UV exposure, However, certain forms of vitamin A found in sun protection products—namely retinyl palmitate, a combination of retinol (vitamin A) and palmitic acid, an ingredient found in tropical plants such as palm and coconut—can be cause for concern. When exposed to the sun's UV rays, retinol compounds break down and produce destructive free radicals that are toxic to cells, damage DNA, and may lead to cancer. In fact, FDA studies have shown that retinyl palimitate may speed the development of malignant cells and skin tumors when applied to skin before sun exposure, so steer clear of skin sun products that harbor the stuff.
Homosalate This UV-absorbing sunscreen ingredient helps sunscreento penetrate your skin. Once the ingredient has been absorbed, homosalate accumulates in our bodies faster than we can get rid of it, becomes toxic and disrupts our hormones.
Octocrylene When this chemical is exposed to UV light, it absorbs the rays and produces oxygen radicals that can damage cells and cause mutations. It is readily absorbed by your skin and may accumulate within your body in measurable amounts. Plus, it can be toxic to the environment.
Paraben Preservatives Associated with both acute and chronic side effects, parabens (butyl-, ethyl-, methyl-, and propyl-) can induce allergic reactions, hormone disruption, developmental and reproductive toxicity. While butylparaben was reported to be non-carcinogenic in rats and mice, but it has been previously suspected that parabens and other chemicals in underarm cosmetics may contribute to the rising incidence of breast cancer.
Source of info Womens Health