Sunscreen With Micronized zinc oxide
There has been some concern amoungst rosacea sufferers about possible health problems with micronized zinc oxide and titanium dioxide. An article was published in 1997 with an alarmist title “Titanium Dioxide/Zinc Oxide nanoparticles from sunscreen are found to cause free radicals in skin cells, damaging DNA” Oxford University and Montreal University, Dunford, Salinaro et al.
Dr. Linda Sy, who is responsible for the rosacea friendly sunscreen ZincO Cream (which is composed of 14.5% micronized zinc oxide dimethicone) has responded with some studies that show that dimethicone coated micronized zinc oxide, is photostable when exposed to UV radiation. Thus declaring that ZincO Cream is safe to use.
1. June 2005 – P. Kullavanijaya MD & H. Lim, MD; “Photoprotection” Journal of the American Academy of Dermatology, Volume 52.
“Microfine ZnO (Z-cote) is becoming more popular because it is shown to protect over a wide range of UVA including UVA1 (up to 380 nm). It is photostable and does not react with other organic sunscreens.It is more effective in UVA protection than microfine TiO2, which protects against UVB and UVA2, and is less protective against UVA1. TiO2 has higher refractive index (2.6) than ZnO (1.9), which makes TiO2 whiter (even though the particle size is smaller) and more difficult to incorporate into products that are minimally visible to the eyes. Moreover, TiO2 is more photoreactive than ZnO. Photoexcited micronized TiO2 has been shown to cause cell death in vitro, although no evidence exist on its in vivo toxicity.
A consequence of the photochemical reaction is that it causes TiO2 and ZnO to be less effective as sunscreens. Therefore, TiO2 and ZnO particles are frequently coated with dimethicone or silica, which has been shown to be stable during the manufacturing process and after application of the product on the skin, therefore, the efficacy of these inorganic filters can be maintained.”
2. Jan. 1999 – Mark A. Mitchnick et al; “Microfine zinc oxide (Z-Cote) as a photostable UVA/UVB sunblock agent”; Journal American Academy of Dermatology; Vol 40:85-90.
3. 1998 – Yamamoto et al, ” Formation of singlet oxygen upon UV-irradiation of microfine oxides and its prevention by surface-coating.” Proc. of IFSCC Congress, Cannes, 1998.
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