To date, there is no scientific evidence to suggest that castor oil can help the eyelashes grow. However, it may help make the eyelashes appear thicker or glossier.

Castor oil is a vegetable oil that comes from the seeds of the castor oil plant. There are different types of castor oil, depending on the processing method.

One study from 2003 showed that castor oil increased the “luster” of hair, which might suggest that the same is true for eyelashes.

In the sections below, we discuss the types of castor oil and whether they work to improve the appearance of the eyelashes. We also cover how to use it and consider the risks associated with castor oil use.

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It may be best for a person to use a high quality, pure castor oil on their body and hair.

Jamaican black castor oil is darker due to the manufacturers roasting the castor seeds first, before extracting the oil. In contrast, cold-pressed castor oil does not use heat in the process and is pale yellow with a mild odor.

Although there has been no scientific research into which specific castor oil is best to use for eyelash treatment, anecdotal usage on the eyelashes has included both types.

There is also hydrogenated castor oil, which manufacturers process with hydrogen to make it solid at room temperature. Hydrogenated castor oil is in many cosmetic items.

High quality, pure castor oil may be best to use on the body. These types may have better safety and effectiveness.

All types of castor oil contain similar properties, which may help improve the appearance of the eyelashes.

Castor oil contains 90% ricinoleic acid, according to a study in the International Journal of Science and Research.

Ricinoleic acid contains high levels of triglycerides, which may help moisturize eyelashes. Also, the oil contains omega-6 fatty acids, which may help improve the health of hair.

One 2015 study found that ricinoleic acid was a potential prostaglandin D2 inhibitor, which means that it may be useful in preventing hair loss.

Other research has found higher levels of prostaglandin D2 in balding scalps compared with those with more hair. In 17 men with male pattern baldness, there were higher levels of prostaglandin D2 in the bald scalps than in the scalps with hair.

The International Journal of Science and Research study also suggests that applying castor oil to the eyelashes can increase blood circulation to the hair root and encourage new growth.

There are no scientific guidelines for using castor oil on the eyelashes. However, anecdotal research suggests trying the following methods:

  • Make sure to do a patch test — by applying a small amount to a small area of skin, such as the arm, to test for any allergic reaction — the day before using castor oil on the eyelashes.
  • People can mix the castor oil with a carrier oil, such as coconut or almond oil, or use it by itself.
  • Clean the eyelashes so that they are free of any dirt or makeup.
  • Dip a cotton swab into a small amount of castor oil and run it on top of eyelashes, all the while making sure that none drips into the eyes.
  • Apply the castor oil before bed and wash off it in the morning using warm water and a clean towel.

If a person experiences an allergic reaction, such as a rash or itchiness, they should wash off the castor oil and stop using it. If symptoms persist, it may be a good idea to see a doctor.

Castor oil is present in many cosmetic products, including lipsticks and skin care products. Scientists have found castor oil to have low toxicity, and other research has found 100% concentration of hydrogenated castor oil safe for use in cosmetics.

That said, it may trigger an allergic reaction, such as skin irritation, in some people.

People should test castor oil on an area of skin away from their eyes and face before using it on their eyelashes. If people experience any irritation from the castor oil, they should wash it off and stop using it.

People should try to avoid getting castor oil in their eyes. The American Academy of Ophthalmology recommend using sterile products for the eyes, and people should always follow the advice of their doctor or ophthalmologist when using products on or near the eyes.

People should also take care when ingesting castor oil, as it is a laxative and can cause diarrhea.

Pregnant women should also avoid taking castor oil, as it can induce labor.

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Some people have reported that Latisse causes dry or itchy eyes.

The Food and Drug Administration (FDA) have approved Latisse for enhancing eyelash growth. Latisse is a prescription medicine that increases the length, thickness, and darkness of eyelashes.

Latisse contains a solution of bimatoprost, which is generally safe when people apply it to the base of their eyelashes.

However, some reported side effects of Latisse include:

  • hyperpigmentation of the eyelids
  • red eyes
  • dry or itchy eyes

These side effects should pass when people stop using Latisse. However, one potentially permanent side effect of the medication is a darkening of the iris.

According to the American Academy of Ophthalmology, people with existing eye conditions — such as conjunctivitis, macular edema, or uveitis — should not use Latisse.

People who wish to use Latisse should check with their doctor or ophthalmologist to ensure that it is safe for them to use.

There is no scientific research to support the theory that castor oil will make eyelashes grow longer or thicker. However, it may help increase the luster of eyelashes, making them appear thicker and glossier.

People should try to avoid getting castor oil in their eyes, and they should stop using it if it causes any irritation.

People with an existing eye condition should speak to their doctor before using castor oil on their eyelashes. There are alternatives, such as Latisse, available.