Green tea oil, also known as camellia oil or tea seed oil, is known to be rich in antioxidants and catechins that help reduce dihydrotestosterone (DHT), a hormone that can shrink your hair follicles.
A huge plus is that it's one of the least greasy of the bunch and can absorb into the scalp quickly, making the oil ideal for application. If you don't have the essential oil on hand, you can alternatively opt for a green tea rinse. To apply, simply steep the tea bags in some water and cool for 30 minutes to an hour before pouring the tea into either a spray bottle or an oil applicator bottle.
Rosemary oil for hair growth has a lot of street cred going for it. A clinical review published in BMJ found that when massaged into the scalp daily, rosemary can help with hair growth.2 This was further confirmed by another study published in SKINmed Journal, which discovered that it can also protect against hair loss.3 "Rosemary effectively promotes hair growth and reduces hair loss by soothing the scalp and stimulating new hair growth," says Gillen. "In fact, it's commonly used to treat alopecia." To apply, mix a few drops of rosemary oil with your favorite hair oil and massage it into your hair and scalp a few times per week.
A 2017 study in the BMC Complementary and Alternative Medicine found that this flower extract has major potential as a hair growth product.4 Why? The oil was found to regulate sebum production and maintain secretions around your hair follicles. It's also chock-full of amino acids, which have been shown to nourish the hair and boost blood circulation.
"Geranium is an effective antibacterial, antimicrobial, and anti-inflammatory, making it an all-around amazing skincare product," says Gillen. "It can also help strengthen, hydrate, and restore your hair." Application rules are the same as the above—either dilute it with your hair care products or massage a couple drops of geranium oil to your scalp a few times per week.
First things first: According to Korab, when it comes to castor oil, there is very little scientific research that it actually helps hair grow. The benefits of castor oil for hair growth are mainly anecdotal, but that is worthy enough of giving it a try—especially considering its long history of use. The idea is that its high content of ricinoleic acid can help improve blood circulation in the scalp. The humectant is also composed of a powerful mix of fatty acids (read: super moisturizing), and as we know, moisturized hair is more likely to grow at a faster rate.
"Castor oil is one of the few oils that I have found actually works," says Gillen. "It can penetrate all the way down into the hair follicle while other oils may penetrate slightly but won't reach the inside of the follicle." Gillen also adds that you must apply castor oil directly on the scalp or skin. "I like to use a mascara wand to apply the castor oil on my hairline and a gel liquid liner brush to apply along my eyelids (for lash growth)."
The menthol in peppermint oil causes vasodilation of the blood vessels—meaning it causes blood vessels to widen, increasing blood flow.5 And blood flow is essential to successful hair follicle growth. If you have oily hair, peppermint also balances the pH of your scalp, which can help regulate your oil production. Just one thing to keep in mind: According to Gillen, peppermint oil should always be mixed/diluted with a carrier oil—never apply it raw to your skin.
