We know, we know: we keep hearing about this miracle hair oil that revitalizes hair, wipes out buildup, and changes hair forever. But before you dismiss castor oil as another beauty craze, remember that this ingredient has centuries of history, dating back to ancient Egypt. What's more, dermatologists and hair experts endorse it as an effective way to moisturize dry hair and promote healthy hair growth. We were curious too. So we asked the experts for more information.

If you look at the molecular structure of castor oil, you will see that it is glycerol with long chain fatty acids. Why is that important? According to Atlanta-based dermatologist Tiffany L. Clay, M.D., fatty acids are excellent for nourishing hair follicles. The outer layer of the hair shaft is covered with a scale-like structure called the cuticle, but when hair is damaged, it flakes and peels off, causing frizz and dullness. But hope is not lost! Clay points out that "castor oil can seal and flatten the cuticle."

To apply the oil, Clay recommends warming a small amount in the palm of your hand and blending it along the ends of your hair once a week. Just be careful not to overuse it. Castor oil is quite thick, and using too much can make hair feel wet and greasy.

If you are not comfortable using pure castor oil for fear of overdoing it, there are several less intense options, including shampoos, conditioners, hair masks, and serums.

Yes and no. Castor oil "has been shown to help topical products penetrate better and grow hair," says Davar G. Banusari, M.D., a New York City-based dermatologist who specializes in hair loss. 'That said, I don't think there is any scientific evidence to claim anything particularly grandiose like it stimulates new hairs.'

If you think of the scalp as a garden, you would agree that a well-watered and fertilized garden produces better tomatoes than a dusty, unkempt garden. Yes, castor oil moisturizes and nourishes the scalp, resulting in stronger, shinier, healthier hair. But it does not increase the number of hairs. This is an important distinction.

But don't be discouraged if castor oil is not effective in stimulating new hair growth. Says Vanusari, "I can't stress enough how important it is to see a certified dermatologist when it comes to hair loss." 'There are so many new options now, and it's much easier to develop a comprehensive plan for early hair loss than it is later in life.'