Castor oil.

"It's very viscous. There's no evidence that it grows your eyelashes, there's no evidence that it grows your hair, but a lot of people find that their hair looks like it's growing when they put it on. I have always thought a lot of that has to do with the fact that it's so viscous. It coats the hairs and makes them look thicker. I don't have a study or any clinical trials showing castor oil for hair growth. It's relatively harmless unless you develop contact dermatitis to it."

"Ricinoleic acid is kind of one of the more active components within castor oil. First and foremost it's a laxative if you ingest it. It's got a lot of moisturizing properties to it, it's very viscous, it's very hydrating. So putting it on the skin, it's no surprise that people find that it makes their skin look better. I believe them when they say that because it is very moisturizing. My biggest concern is it can cause a contact dermatitis. Anything you put on your skin can cause a contact dermatitis, but it's definitely something that happens to a lot of people and something I think people experience and may not realize that it's the castor oil that is the problem. Castor oil is put in a lot of skincare products as an ingredient, and the way it comes up in dermatology is patients come in and they've developed an allergy to it. But you can become allergic to anything or irritated by anything, so is it really that much of an issue for everyone? It's hard to say."