Hair Growth Serum: A Definitive Guide

  • Medically reviewed by:
  • Written by: William Slator
  • Last updated: 26/02/2024

There are so many hair growth products on the market, and it can be difficult to narrow your options to just one or two. With so many formulations to choose from, where should you begin?

In this article, you will learn more about what a hair growth serum is. This includes how they work, what ingredients to look for, and how to apply them effectively.

What is Hair Growth Serum?

A hair growth serum is a liquid formulation that is applied topically to the scalp and hair. Its purpose is to promote hair growth, though the way it does so will vary by ingredients.

How Hair Growth Serum Works

Hair growth serums are a broad class of hair care products that attempt to grow hair in various ways. Let’s take a look at some of the more common mechanisms that hair growth serums use.

Blocks DHT

If you suffer from pattern baldness, also known as Androgenetic Alopecia, you have likely heard of Dihydrotestosterone (DHT).

DHT is an androgen hormone largely responsible for the development of secondary sex characteristics in men. This means it is found abundantly within males though it exists (at a much smaller rate) in females, too.

For those with pattern baldness, though, a sensitivity to DHT at the hair follicles may cause an unwelcome effect – hair loss.

One way that hair growth serums work is to block DHT.

In those with hair follicles sensitive to DHT, a process called hair follicle miniaturization occurs. The follicles become inflamed in the presence of DHT, which leads to chronic inflammation of the follicle. As such, the hair is unable to fully grow and, eventually, the follicle will die.

Hair follicle miniaturization caused by DHT

The logical course of action, then, seems to be to block DHT. While this will ensure that hair follicle miniaturization does not occur, it can also have some negative effects.

That is not to say that blocking DHT does not work, as is evidenced by the popularity of the FDA-approved hair loss drug finasteride. Blocking DHT can be an effective way to regrow your hair. But you will want to consider all potential side effects before you proceed.

Increases Blood Circulation

The hair follicle miniaturization process was briefly covered above, but one aspect that is often not discussed is that of poor blood circulation.

As the hair follicle becomes inflamed, the follicle itself has less room for hair to grow within it. But the follicle is also slowly being choked off from its blood supply which is found at the very base of the follicle.

When this happens, the hair growth process will also slow down considerably. After all, how can the follicle produce cells for hair growth when its source of oxygen and nutrients is being strangled?

So not only is there less room for hair growth, but there are also fewer resources available.

Instead of (or in addition to) blocking DHT, you can attempt to circumvent the effects of DHT sensitivity by increasing blood flow to the follicles. This does not treat the issue, but instead, it makes it possible for the hair follicles to thrive in the presence of DHT.

The good news is that the ingredients and techniques used to increase blood circulation are also often used to reduce follicular inflammation. This means that 1) your hair follicles are receiving more adequate blood flow even despite follicle miniaturization, and 2) the hair follicles can take in the blood flow effectively.

Reduces Scalp Calcification

It is difficult to discuss hair follicle miniaturization and inflammation without discussing scalp calcification.

Scalp calcification occurs as a result of long-term, untreated hair follicle miniaturization. As the hair follicles receive less blood, the follicles will slowly die. This can then lead to fibrosis and eventually scalp calcification.

Scalp calcification reduces blood flow to hair follicles which causes miniaturization and eventually follicle death.

The true cause of scalp calcification is excess calcium deposits. This is a known side effect of long-term poor blood circulation. While restoring that blood flow will help to reduce the calcium deposits, it will not necessarily reverse the established calcification.

Ingredients to Look for in a Hair Growth Serum

With so many serums to choose from, you may find yourself suffering from analysis paralysis. One way to narrow your options, though, is to consider only those products with the most effective ingredients.

While not an exhaustive list, the below ingredients are some of the most effective when it comes to promoting a healthy scalp environment and stimulating hair growth.


As mentioned above, one of the ways that hair growth serums work is to increase blood circulation. One ingredient which is commonly used to this end is minoxidil.

Minoxidil is an FDA-approved hair loss topical with various mechanisms. It works to increase blood circulation to the immediate area, though there are other suspected mechanisms as well.

The most common way to use minoxidil for hair growth is as a standalone product. You will have likely seen Rogaine and various generic formulations at your local pharmacy or advertised on television. But did you know that minoxidil is also often added to hair serums and elixirs?

The reason for the addition of minoxidil is simple: it has been proven for decades to be an effective hair growth stimulator (1).

You can find many serums online and in stores that list minoxidil as an active ingredient. The formula will often also contain other beneficial components, like vitamins and carrier oils.


A common theme you will come across in the hair loss community is the idea that poor nutrition is the cause of hair thinning and loss. It is not the only cause, but poor nutrition can certainly contribute to poor hair health.

One of the most common supplements recommended to those with hair thinning and loss is niacin.

Niacin is a B vitamin (B3) also known as nicotinic acid, niacinamide, and nicotinamide (2). It occurs naturally in many foods, including greens, poultry, fish, and eggs (3).

Niacin is needed in almost all tissues within the body as it converts carbohydrates into the energy that cells need to perform basic metabolic functions. But what about its role in hair?

Hair growth is a function just like any other. It requires energy to occur, which is why niacin is so crucial to healthy hair growth. That is not the only role that niacin plays, though. Research suggests that the B vitamin may reduce inflammation and promote blood circulation (4, 5).


It is not often that you will see niacin discussed without mention of another important hair vitamin — biotin.

Biotin is another B vitamin (B8) that plays a significant part in metabolic processes. It mainly works to metabolize fats and carbohydrates (6). This influences cell growth and protein synthesis, both of which are necessary for hair growth.

While you want to ensure you are eating enough foods with biotin, you may also want to consider topical application.

Walnut smoothie

There are plenty of hair growth serums that incorporate both niacin and biotin in their formulas. These help to strengthen hair while simultaneously supporting the hair growth process.

Saw Palmetto

Saw palmetto is a plant that was originally used by Native Americans to treat ailments. In more recent years, its use as a treatment for pattern hair loss has become obvious (7).

Just like finasteride, saw palmetto is a 5-alpha-reductase inhibitor. It works to slow DHT production.

When taken orally, saw palmetto can cause side effects similar to finasteride. When applied topically, however, the risk of these side effects is significantly reduced.

Eclipta Alba

Eclipta Alba (E. alba) is a popular herb used in many Eastern countries such as India, China, and Thailand. For centuries, the herb has been used to treat an array of maladies.

Of particular interest to hair loss sufferers may be its anagen-promoting effects, as well as its anti-inflammatory properties.

In one study performed on nude mice, E. alba was shown to induce hair growth by promoting the transition from telogen (resting) phase to anagen (active growth) phase (8)

The results of this particular study suggest E. alba may “improve[] the disordered keratinization of nude mouse hair follicles.”

The cause of hair loss in men and women with pattern balding is not due to disordered keratinization. However, a treatment that promotes the transition from telogen to anagen phase is still extremely beneficial.

In addition, the anti-inflammatory properties of E. alba will ensure that further pattern balding, which is triggered by miniaturization of the follicle as a result of inflammation, is unlikely to occur. In this way, follicle miniaturization may reverse naturally as inflammation is treated.


When it comes to pattern baldness, a particular concern is the calcification of the scalp tissues. This occurs as a result of long-term follicle miniaturization which leads to poor blood circulation.

As a free amino acid, taurine is unique. This amino acid is found abundantly in tissues, particularly within skeletal muscles (9).

Taurine has a few roles, including 1) calcium channel modulation; and 2) antioxidant activity.

As mentioned, scalp calcification is a serious concern for people with pattern baldness. This occurs as a result of long-term balding, and it can mean death to the hair follicles if not treated quickly.

Calcification is the process by which large calcium deposits exist on the scalp. These calcium deposits result in toughening of the skin which further contributes to the decline of a hair follicle’s growth capabilities.

If left untreated, calcification will result in fibrosis which is the permanent hardening of the tissues.

Taurine is a calcium channel modulator. It maintains appropriate calcium homeostasis (10).

While the body manufactures taurine naturally, it will use it in areas where calcium homeostasis is most critical to life (e.g. heart, brain). So how can you benefit from taurine’s calcium-modulating effects on the scalp? By using it as part of your hair care routine.

When applied directly to the scalp, taurine can be used to combat scalp calcification. Its absorption through the skin will also lend itself to further scalp health, as it is a known anti-inflammatory and antioxidant (11).


Adenosine is an organic compound that occurs naturally. It is most commonly found as one of its derivatives, including adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP).

Perhaps the most well-known derivative is ATP. This molecule stores and delivers the energy that our cells need to perform basic functions. And as a basic building block of RNA, there is no denying that adenosine plays a key role in many important functions. So, what about hair growth?

A few studies on adenosine and hair growth have been performed in recent years. One study found that topical adenosine increased anagen hair growth and thickened hair in Japanese women with pattern baldness, while another found it was comparable to minoxidil in treating hair loss (12, 13).

There are two mechanisms by which adenosine is thought to be beneficial for hair loss sufferers:

  1. It increases fibroblast growth factor 7 in dermal papilla cells.
  2. It has a vasorelaxant effect.

While further studies are needed on adenosine and hair growth, there do not appear to be any safety concerns when the compound is used topically (14).


Caffeine is a stimulant found in coffee, tea, chocolate, soda, over-the-counter and prescription drugs, and even hair care products.

The organic compound stimulates the central nervous system to temporarily enhance performance. As recent studies have shown, the compound may also contribute to hair growth when used topically.

There are a few ways in which caffeine is thought to contribute to hair growth. For example, the stimulant may:

  1. Suppress DHT (15)
  2. Elongate the hair shaft (16)
  3. Prolong anagen (active growth) phase of the hair growth cycle (17)

When applied topically, the compound has also been shown to effectively penetrate the hair follicles (18). This makes it an ideal addition to any hair growth topical formula.


Tretinoin, a synthetic form of vitamin A, is also known as a retinoic acid. Its main topical use is in the treatment of acne and sun-damaged skin (19).


Melatonin is a hormone naturally produced by the body that regulates the sleep-wake cycle (20). For those with insomnia or other sleep issues, melatonin can also be taken as a supplement.

But did you know that melatonin has also been shown to be beneficial in promoting hair growth?

There are two mechanisms believed to contribute to melatonin’s hair growth benefits.

First, melatonin has been shown to induce anagen phase hair growth, particularly in females.

In one study on the topic, the percentage of hairs in the anagen phase in the occipital region of females with pattern baldness was shown to increase from 76.3% to 85.0% after 6 months of treatment (21). The results weren’t as drastic on the hairline, though increases were seen there, too (82.2% to 83.8%).

These benefits were observed in numerous studies throughout the years (22).

Second, melatonin is a known antioxidant (23). This means melatonin reduces oxidative stress by reducing free radicals in the body.

What does this mean for hair growth?

Oxidative stress can impact the hair growth process, and free radicals may damage structures (by stealing electrons from nearby molecules) like the hair follicle.

With a topical antioxidant like melatonin, you can keep oxidative stress at bay.

Minoxidil: The Original Hair Growth Serum

With so many hair growth serums on the market, it can be difficult to choose the “right” one. But before so many of these serums made it to the market, the one and only real contender for hair growth serum was minoxidil.

Minoxidil was originally developed as an oral drug for use in treating hypertension (high blood pressure) (24). It was during the clinical trials that one unexpected side effect was noted: hair growth.

As is the case with many prescription drugs, the hypertension tablet Loniten (minoxidil) was soon being prescribed by doctors for off-label use as a hair loss treatment. As more evidence to back up minoxidil’s safety and efficacy was collected, the drug was soon changed to a topical formulation.

And in 1988, topical minoxidil (marketed under the brand name Rogaine) was finally approved by the FDA for hair growth.

Rogaine vs generic minoxidil

So how does minoxidil work?

There are three suspected mechanisms for minoxidil’s efficacy. The topical hair loss drug is thought to:

  1. Increase blood circulation to the hair follicles by activating potassium channels and reducing calcium levels.
  2. Upregulate the expression of Vascular Endothelial Growth Factor (VEGF) in human hair dermal papilla cells.
  3. Prolong the anagen (active) phase of hair growth.

Minoxidil does NOT block DHT or interfere with 5-alpha-reductase. This is great news for anyone who has previously tried finasteride but quit due to the side effects.

How to Use Hair Growth Serum

When using hair growth serum, the ability of the product to distribute evenly throughout the scalp is all in the application process. For best results:

  1. If you will be applying after a shower, towel dry your hair as usual. You can also apply it to a dry scalp.
  2. Divide your hair into four equal parts.
  3. Using a dropper or the applicator tool provided with the serum, apply a few drops to each section.
  4. Use your fingertips to gently massage the serum into the scalp.

You should repeat these steps as many times per day or week as the directions on the serum packaging indicate.

Tips for Making Your Hair Growth Serum More Effective

Do you want to get the most out of any hair growth serum? Of course, you do! Take a look at the tips below.

Apply It With Scalp Massage

If you want to get the most from your hair growth serum, there’s one thing that’s almost as important as its ingredients: the application process.

The way you apply your serum can have an impact on the efficacy of its delivery.

By applying your hair serum while also performing a scalp massage, you ensure the serum is spread evenly throughout your hair and scalp.

But scalp massage also has benefits of its own.

First, it’s an effective way to promote blood flow to the hair follicles (15). This ensures the follicles are receiving the oxygen and nutrients they need, while also getting waste and excess DHT removed.

Scalp massages improve blood flow and thereby increase the amount of nutritive substances reaching the hair follicle

Second, scalp massage can help to reduce scalp tension which is thought to be a major trigger for pattern baldness.

To learn more about scalp massage techniques, go here.

Keep a Consistent Schedule

Do you want to see results? The hair growth results promised by many hair serums may seem too good to be true. And while outcomes will vary, the best way to ensure results is by keeping a consistent application schedule.

The serum you use can have the best ingredients with scientifically proven results, but without a consistent application schedule, you are just throwing the opportunity away.

This is why you must add the hair growth serum to your daily self-care routine.

So let us say you stick to a consistent schedule. How long until you can expect to see signs of new hair growth?

This will depend on many factors, such as the cause and severity of your hair loss. In general, though, it can take three to six months to begin to see visible results. Patience is key.

Use It With Finasteride

There are only two drugs that are FDA-approved for hair growth: minoxidil, and finasteride.

As mentioned above, minoxidil is a topical treatment that has various mechanisms associated with its efficacy. Finasteride is an oral drug with a very different approach to combating hair loss.

Finasteride is a 5-alpha-reductase inhibitor (25). This is the enzyme responsible for testosterone’s conversion to DHT. By inhibiting 5-alpha-reductase, you lower systemic DHT levels. This means less DHT at the scalp and, presumably, less thinning and hair loss.

Some hair loss sufferers prefer one approach over the other. But many people use both FDA-approved hair loss treatments at the same time to improve or hasten results.

Before you take this approach, it’s important to educate yourself on the risk of side effects.

As with any medication, finasteride does come with some risks (26). The good news is that these side effects are unlikely to be severe or life-threatening. They will also resolve themselves once the medication is discontinued.


Hair growth serums can be a great addition to your hair care routine. They are easy to use, and they offer a simple way to promote a healthy scalp environment.

Should hair serum be the only tool in your hair growth arsenal? Of course not. A multi-pronged approach is the best way to combat hair loss. But if you are just getting started, then adding a hair growth serum is a step in the right direction.

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