Research Team

Castor Oil for Hair Growth: Everything You Need to Know

Castor oil has been used as a natural remedy for thousands of years dating back to the Egyptians in 1500 BC, where it was known to have laxative and anti-inflammatory effects (1).

However, in recent years more studies have been done into the hair-boosting effects of Ricinoleic Acid, a key component of castor oil, as well as the hair-growth inhibiting compound Prostaglandin D2 (PGD2).

In this article, we’ll go into the science of why castor oil should become a potent tool in your arsenal. We’ll also show you how to incorporate it easily into your daily hair care routine.

As well as being a low-cost alternative to commercial hair loss treatments, it’s 100% natural so you won’t have to worry about any nasty side effects from chemicals.

I think you’ll agree that castor oil sounds great on paper, but is it really as impressive as the studies make it out to be? Let’s find out.

What Is Castor Oil?

Castor oil, with its distinctive taste and odor, is a vegetable oil that has been extracted from castor beans.

It’s commonly used as a preservative in foods such as wheat and rice, and as an effective over-the-counter laxative.

While castor oil is perfectly safe to consume, the castor beans used in its manufacturing process are extremely toxic and can be fatal if consumed. Due to the presence of ricin, which is destroyed in the heating of the seeds to make oil, eating just a few of these seeds is enough to cause death.

Keep this in mind if you’re trying to cut out the middle man and start harvesting your own castor oil.

The reason why castor oil has become so popular in the hair loss industry is due to its high concentration of ricinoleic acid, which makes up 90 percent of its fatty acid composition.

Ricinoleic acid has been widely studied for its anti-inflammatory properties (2) and for its effective treatment of bacterial infections (3).

When your scalp is inflamed, your body is unable to transport vital hair-growing nutrients to the follicles. This can result in thinner hair, slower growth, and is cited by a large number of studies as a possible cause of alopecia areata (4, 5, 6, 7).

The Science Behind Castor Oil

In this section, we’ll go in-depth into some scientific studies focusing on the following benefits related to castor oil:

  • The effects of PGD2 on hair growth;
  • Whether PGD2 is solely to blame or is something else at play;
  • Ricinoleic acid and its effect on prostaglandins;
  • How pH balance impacts hair growth and why ricinoleic acid can help this balance.

Up until this point I’ve made some pretty bold claims in favor of castor oil. However, claims without real scientific data to back them up are near enough useless.

As a result, our aim in this section is to present you with the scientific evidence both for and against castor oil.

From this, you’ll be able to make your own informed decision as to whether it’s right for you.

The Effects of PGD2 on Hair Growth

PGD2 is a mediator produced by mast cells, and it has been shown to have major inflammatory effects within the body (8).

There are also a number of less-than-desirable side effects associated with this compound (9, 10, 11, 12).

These include:

  • A critical role in the development of allergic diseases such as asthma and eczema.
  • An increase in blood pressure due to vasoconstriction within blood vessels.
  • The constriction of bronchial airways, especially in asthma sufferers.
  • A major contributor to androgenic alopecia (AGA) in men.

The stand-out side effect on this list, however, is the link to PGD2 and hair loss.

Eighty percent of Caucasian men will experience some degree of AGA before the age of 70, and Dihydrotestosterone (DHT) has always been considered a leading cause of baldness (13).

However, more studies are being done into the effects of PGD2 on hair growth, and research shows that PGD2 may play a more pivotal role in causing baldness than DHT.

In 2012, a study carried out by Garza et al showcased the effects of elevated levels of PGD2 on hair loss (14).

An initial test was made comparing the levels of PGD2 in haired and balding scalps.

Through the use of immunoassay, the team discovered a significant increase in absolute levels of PGD2 between the two groups – 16.63 ng/g and 1.5ng/g in balding and haired scalps respectively.

Other prostaglandins were also tested including 15-dPGJ2, a dehydration end product of PGD2. While absolute levels of these compounds weren’t as high as PGD2, a notable difference was found in the concentrations between haired and balding scalps.

In order to prove their hypothesized link between PGD2 and hair loss, the team first carried out tests on mice and later on human hair.

After synchronizing the hair follicle cycles of nearly identical mice through the topical application of 15-dPGJ2, 10µg of 15-dPGJ2 was applied every other day.

Hair length was measured regularly for 20 days together with an acetone vehicle as a control.

Alongside this experiment, 1µg of PGD2 and 15-dPGJ2 were applied to separate subjects in order to establish an effective minimum dose.

The results showed a notable reduction in hair length for both PGD2 and 15-dPGJ2 compared to the acetone vehicle. This clearly defined PGD2 as an inhibitor of hair growth in those suffering with AGA.

Clearly then, when we are looking at potential treatments for hair loss, shouldn’t we try to inhibit PGD2 as much as possible?

Is PGD2 Solely to Blame for Hair Loss?

When considering the merits of one product compared to another, it’s always useful to critique its claims.

In this case, we should look at whether or not PGD2 is the cause of hair loss, or if hair loss causes an increased production of PGD2.

PGD2 is actually a crucial component of the male reproductive system. Unfortunately, as is the case with every bodily process, mistakes can happen.

This is where another prostaglandin, PGE2, comes into play.

PGE2 is a potent activator of the cyclic monophosphate/protein kinase (cAMP/PKA) signaling pathway and causes G-proteins within your cells to either activate or inhibit cAMP (15).

Cyclic AMP is a key regulator in cell growth and tissue regeneration, and due to its pro-inflammatory effects a natural balance is required (16). A balance which is maintained by PGE2 (17).

Therefore, you have the hair-growing effects of PGE2 competing with the hair-thinning effects of PGD2. This causes problems to occur when an imbalance between the two is created.

When an imbalance occurs the GPR44 receptor is triggered, and that’s when we start to see unwanted issues such as alopecia.

This begs the question; what can we do to keep a healthy balance of the two prostaglandins and prevent the receptors from getting triggered?

Ricinoleic Acid and Its Effect on Prostaglandins

As we discussed earlier, ricinoleic acid is an omega-9 fatty acid that also makes up roughly 90 percent of castor oil.

Although the number of studies done into the efficacy of ricinoleic acid as a hair loss treatment are still quite small, there are some interesting results coming from areas such as China – where traditional medicine is still quite prevalent.

A recent study by Fong et al looked into the effects of traditional Chinese remedies on inhibiting prostaglandin D2 synthase (PTGDS), the catalyst for converting PGH2 into PGD2 (18).

In this test, the team studied the constituent components of 12 different herbs by docking them into six different PTGDS structures.

Docking is a method used in molecular modelling that predicts the preferred orientation between two molecules that would put them in their most stable state.

Think of it like putting a glove on a hand. There are plenty of ways to put on a glove, and some work better than others, but there’s one orientation that is preferred over the rest.

When these molecules are taken through the experimentation process they are tested in for validity with current data, and then given a docking score based on how well they fit together.

In the case of Fong’s study, they discovered that many of the herbs’ constituents could bind more effectively than currently proven PTGDS inhibitors. However, they lacked the permeability of other treatments and as a result were given less emphasis in the final results.

One of the compounds that exhibited a great balance of PTGDS inhibition, permeability, and minimal skin reactions was ricinoleic acid.

More research needs to be done into its efficacy as a hair-loss product, but the initial data seems very promising.

How pH Balance Impacts Your Hair Growth

An often overlooked area of developing healthy hair is maintaining the ideal environment to spur on growth.

This includes paying close attention to the delicate balance of pH levels within the body.

The body thrives in a neutral environment of roughly 7.4 on the pH scale. Where 1 is acidic and 14 is alkali.

However, your scalp has a pH of between 5.4 and 5.9 (19). This is to prevent the growth of fungi and bacteria and allows the cuticles to remain closed, resulting in strong and healthy hair.

The issue is, most commercially available shampoos fall between 6.0 and 7.0 on the pH scale (19).

Common conditions such as dry scalp, eczema, and fungal infections are linked to an alkaline environment (20).

One study notes that using products that are slightly more acidic, around 5.5, could be relevant in treating certain skin conditions (21).

This is why incorporating something like castor oil, which contains a large percentage or ricinoleic acid, might be beneficial in maintaining healthy hair.

What Are the Side Effects of Castor Oil?

Throughout history castor oil was used as a harsh method of both punishment and torture, especially during the 20th century.

It acts as a powerful laxative, overconsumption could result in malnutrition, and is used as a commercially available laxative throughout the world today.

But unless you plan on drinking bottles of the stuff, you have nothing to worry about. There are, however, a few side effects of castor oil worth mentioning.

A very small minority of users may suffer an allergic reaction to castor oil, and it’s advised to rub some of the oil on a small portion of your skin. In the event that you do suffer from itchiness, redness or any unpleasant sensations, you should avoid any further use of the product.

Castor oil is commonly used to induce labor in a non-medical setting. Its safety and effectiveness as a labor-inducing drug is still being researched, with one study stating no side effects were reported in pregnant women yet it showed no significant improvement in time to birth (22).

Also, despite laxatives often being used during pregnancy, some are better than others. Some may cause an increase in blood pressure, while others may negatively affect nutrient absorption (23).

As a result, pregnant women should always seek the advice of a medical professional before use.

How to Include Castor Oil in Your Routine

The consensus is that consumption of castor oil isn’t going to impact your hairline much, if at all.

However, applying it topically to your scalp can be a great way to improve hair quality and bring about some much needed growth.

In this section we’ll go through some ways you can easily incorporate castor oil into your routine.

Creating a Castor Oil Blend

As castor oil is extremely thick compared to other oils, it’s common to mix with other components in order to make it easier to apply and remove.

What you’ll need:

  • Castor oil
  • Another oil of your choice such as jojoba, coconut, or argan
  • Rosemary essential oil or whichever is your favorite


Add your oils to a container in the ratio of 3 parts castor oil to 1 part other oil. We’d recommend starting with 10-15 drops of castor oil.

Place a few drops of your chosen essential oil in with the other ingredients and mix thoroughly for two to three minutes.

Apply a few drops of this mixture into a damp scalp, and work it through your hair with your fingertips until evenly covered. You can also place a towel over your shoulders if you’re worried about getting oil on your clothes.

We’d recommend leaving it in for a few minutes before rinsing thoroughly.

Once you become more competent with the process you may want to leave the mixture in longer, but that’s entirely up to you.

Apply It Directly to Your Hair

This method is very similar to the previous one, but it’s better designed for those of you who don’t want to buy multiple ingredients and spend the time mixing them together.

The downsides of only using castor oil, however, are that it’s difficult to work with and has an unpleasant smell.

If you can look past these then there’s no reason why you can’t use this method instead.

Beginning with a very small amount of castor oil, massage your hair from root to tip until your hair is covered.

You’re not looking to saturate your scalp, just provide a thin, even coating.

Similar to the previous method, you’re free to leave the oil in for three minutes or overnight.

Be sure to rinse thoroughly, and try not to use any harmful shampoos during this process.

Making Your Own Shampoo

There are hundreds of natural shampoos available now for people looking to avoid the myriad chemicals loaded into each bottle.

If you’re looking to save money, with a small time investment, then look no further. This is a great hair-boosting shampoo packed full of ingredients that will leave your hair feeling strong and nourished, as well as fighting hair loss, without any chemicals.

What you’ll need:

  • 30ml of castile or baby soap
  • 1 tablespoon of castor oil
  • 20ml olive oil
  • 2 teaspoons of coconut milk
  • 10ml of honey
  • A few drops of your favourite essential oil

NOTE: Feel free to adapt this recipe to your needs, and experiment with the ratios. Once you’ve found the right mixture for your hair, simply scale up the numbers to make more. Just remember, due to the presence of coconut milk the shampoo will have a shelf-life of 4 or 5 days.


All you need to do is add the ingredients together in a bowl or suitable container, and stir thoroughly.

Once it’s done you should use this in place of your normal shampoo one to two times a week.


PGD2 is an inflammatory mediator that has been linked to slowing hair growth, as well as being a possible contributor to AGA (14).

While PGD2 plays a large role in hair development, studies have shown that creating a balance between PGD2 and PGE2 may also be crucial (15, 16, 17).

Ricinoleic acid, the major component of castor oil, showed promising signs of in vivo PGD2 inhibition in one study. However, more research needs to be done into its viability as a hair loss treatment (18).

Despite this, ricinoleic acid is noted for its anti-inflammatory and anti-bacterial properties, both of which are beneficial in providing a healthy environment for hair (2, 3).

These properties combined make castor oil an effective tool in any individual suffering from hair thinning.

However, don’t expect castor oil to be a magical cure for baldness.

It’s better suited as a treatment to strengthen the hair you currently have, as well as improving the health of your scalp and preventing further hair loss.

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