That being said, the dense oil is also a known irritant and Dr. Zeichner suggests practicing caution if you're planning on trying the DIY hair hack.
"Castor oil is a known irritant. So I am always cautious about recommending it for use around the eyes or eyebrows," he says. "There is a little published data to support its use, and much of what we know comes from anecdotal reports on the Internet."
Since we all know what you Google isn't always reliable, he recommends that if you develop any irritation, burning, or stinging of the skin, to discontinue using it. If you have facial acne, Dr. Zeichner also suggests avoiding castor oil because its thick consistency can exacerbate it.
On your head, castor oil may help with dandruff, which in turn may be stunting hair growth. "Dandruff is caused by high levels of yeast on the scalp," explains Dr. Zeichner. "This results in inflammation of the skin with flaking, and the inflammation may also interfere with hair growth." While anti-fungal shampoos are the best way of treating dandruff, some people have found that due to its anti-inflammatory properties, castor oil has a similar effect.
If you're using it on your scalp, you can apply it and leave it overnight, but since the oil can be irritating, it can be safer to start with short contact therapy. For example, rub it into your scalp as you sing the alphabet, and then rinse it off.
The most harmless route for getting your hair thick and full, is to use shampoo and conditioner specifically formulated for thinning strands. "These products may actually code each individual here to increase thickness and give the hair a fuller appearance," explains Dr. Zeichner. "Using the wrong shampoo and conditioner may actually way the hair down and make it look thinner than it is."
In addition there's a number of over-the-counter oral supplements and treatments that can aid in promoting hair re-growth such as women's Rogaine ($75.99; chemistwarehouse.com) and Evolis's line of line of products that inhibits FGF5, a factor that has been shown to interfere with hair growth