丙二醇對人體有害嗎，点解？？

首先，睇下對丙二醇嘅介紹先。

丙二醇，也稱作1,2-丙二醇，是一種有機化合物（二醇），通常是無味、無嗅、無色透明的油狀液體，吸濕，並易於與水、丙酮、氯仿混合。丙二醇是通過環氧丙烷的水合作用製造。

丙二醇
圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Propylene_glycol_chemical_structure.png/200px-Propylene_glycol_chemical_structure.png
化學名 1,2-propanediol 其他名 propylene glycol 化學分子式 C3H8O2 分子量 76.09 g/mol CAS登錄號 [57-55-6] 密度 1.036 g/cm3 熔點 -59 °C 沸點 188.2 °C SMILES CC(O)CO Disclaimer and references而維基英文版就講到，暫時無足夠證據顥示丙二醇對人體有害。但係最好都唔好涂上皮膚了。可能會allergic的。

Safety The Food and Drug Administration has determined that propylene glycol in or on cat food has not been shown by adequate scientific data to be safe for use. Use of propylene glycol in or on cat food causes the feed to be adulterated and in violation of the Federal Food, Drug, and Cosmetic Act. 21CFR589.1001
The Food and Drug Administration (FDA) has determined propylene glycol to be "generally recognized as safe" for use in food, cosmetics, and medicines. Like ethylene glycol, propylene glycol affects the body's chemistry by increasing the amount of acid. Propylene glycol is metabolized into lactic acid, which occurs naturally as muscles are exercised, while ethylene glycol is metabolized into oxalic acid, which is toxic.
Post menopausal women who require the use of an estrogen cream may notice that brand name creams made with propylene glycol often create extreme, uncomfortable burning along the vulva and perianal area. In these cases, patients can request that a local compounding pharmacy make a "propylene glycol free" cream which is much more tolerable.
Patients with vulvodynia and interstitial cystitis may be especially sensitive to propylene glycol. Women struggling with yeast infections may also notice that some OTC creams can cause intense burning.[1]