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The Role of Testosterone and DHT

It’s easy to demonize dihydrotestosterone (DHT), the male sex steroid hormone identified as the primary cause of 

. However, testosterone and DHT are both critical to the maintenance of overall health and vitality.

In this article, we explain what testosterone and DHT are and provide an overview of how these hormones are produced and regulated by the body. We also discuss the role of these androgens in men’s health and what can go wrong when androgen levels are abnormal. Lastly, we review treatments for low testosterone.

For men who are concerned about male pattern hair loss, these discussions provide an important context for why it’s important to develop 

 that can help avoid broad disruption of androgen levels in males.

Androgens (male sex steroid hormones) serve a number of functions in biological males. They begin the process of sexual development in the womb and help maintain sex-specific traits through adulthood.

Beginning at around 6 weeks gestational age, the testes begin to produce hormones. There are two key types of cells found within the testes: Sertoli and Leydig. Sertoli cells produce a hormone which stops the development of internal female sex organs. Meanwhile, Leydig cells begin to produce testosterone from cholesterol (

).

Testosterone facilitates both primary and secondary sexual development. Primary development refers to processes relating to sexual function and fertility, such as sperm production and increasing libido (sex drive).

Secondary development refers to changes normally observed during puberty. Examples include the emergence of facial, pubic and axillary hair, a deepening voice and increased height and muscle mass (

).

In addition to these physiological changes, research suggests that testosterone may also influence the development of certain brain tissues. This could account for behavioural differences between males and females, such as increased aggression and competitiveness.

How are testosterone and DHT levels regulated?

Testosterone levels in the blood are maintained by a system called the hypothalamic-pituitary-gonadal axis (HPG axis), which is a type of negative feedback loop. The hypothalamus and pituitary gland (located in the brain) are important control points.

The hypothalamus receives sensory input from other parts of the body and uses gonadotropin-releasing hormone (GnRH) to instruct the pituitary gland to release two additional hormones. These other hormones are follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which travel to their target organs in the male reproductive system.

FSH acts on Sertoli cells to support the growth of healthy sperm while LH facilitates testosterone production in Leydig cells. As rising blood testosterone levels are detected by the hypothalamus, the negative feedback mechanism ensures that secretion of FSH and LH decrease accordingly.

Once DHEA and androstenedione are converted to testosterone, the 5-alpha reductase enzyme completes testosterone’s transformation into DHT. DHT has a number of important functions depending on a man’s age.

During childhood, DHT levels typically remain low until the age of 6. With the onset of puberty, LH secretion increases along with testosterone and DHT production.

Increased DHT triggers the growth of facial, pubic and axillary hair and ensures the proper development of external sex organs and the prostate gland (

). As a man ages, DHT also plays a role in prostate enlargement and in susceptible individuals, male pattern hair loss.

Occasionally, testosterone levels may be abnormally low. There are two possible causes of low testosterone (also known as hypogonadism) in men:

Decreased production of testosterone by the testes, or 

Decreased levels of the signaling hormone LH (when LH decreases, this is followed by a drop in testosterone production), also known as 

In men without pre-existing medical conditions, lower levels of testosterone are a natural part of aging. However, the effect of decreased androgens may be more noticeable after the age of 40.

Certain medical conditions such as obesity, kidney disease, diabetes or disorders of the hypothalamus or pituitary gland may also contribute to lower testosterone levels (

Signs and symptoms of low testosterone include:

Gynecomastia (breast enlargement) and breast tenderness

Changes in body composition (increased body fat and/or decreased muscle mass)

Low testosterone is diagnosed with a blood test and a physician’s confirmation of the presence of at least one of the above signs and symptoms.

Thresholds for low testosterone vary regionally. A total testosterone measurement of less than 8 nmol/L (Canada) or 300 ng/dL (U.S.) is generally required. Blood tests for low testosterone are typically done in the morning.

Before a testosterone blood test, it is important for men to refrain from vigorous exercise and/or sexual intercourse for 12 hours prior, as these activities can temporarily increase testosterone levels.

Once low testosterone and related symptoms are confirmed by a physician, there are a number of treatment options. Hormone replacement therapy (HRT) using synthetic testosterone (available as a patch, pill, gel, nasal spray or intramuscular injection) may be considered.

However, use of this kind of medication carries certain risks and must be overseen by a physician experienced in testosterone replacement and men’s health. Side effects are dependent upon dosage and formulation and need to be closely monitored.

Complete blood count and prostate specific antigen (PSA) monitoring, as well as regular digital rectal examinations and blood pressure checks are essential when using testosterone replacement.

In addition to medication, there are a few alternative methods of supplementing testosterone. Research has shown that free testosterone levels can increase with regular exercise, a balanced diet (especially one low in refined carbohydrates), weight loss, increased muscle mass, stress management, reduced alcohol intake and good sleep hygiene.

Vitamin D and minerals such as zinc and magnesium may also be beneficial. Other herbal supplements containing ingredients like 

 have also been shown to have a positive effect on sexual wellness. Research on the long term benefits and side effects (where applicable) of these natural alternatives is ongoing.

The takeaway on testosterone and DHT and men's health

Although it plays a role in pattern hair loss, DHT is one of the building blocks of men’s health and vitality. Because age is generally a factor in the development of low testosterone, it’s important to stay on top of any unusual changes to your health or new symptoms and communicate these regularly to a physician.

Scalp anatomy

When we consider how complex the human brain is, the tissue surrounding our control systems can seem pretty insignificant in comparison.

But in reality, scalp anatomy is rather sophisticated in its own right. The scalp contains 

 that vary in function, form and cellular composition. These delicate membranes and connective fibers contain an intricate network of blood vessels, nerves and hair follicles, among other things. All of this is housed within 5-10 mm of tissue surrounding your skull and central processing system (

 can effectively target hair loss once they have penetrated the outermost layer of scalp skin. Beyond this, drugs like finasteride and dutasteride are more likely to enter the circulatory system through blood vessels found in deeper tissue. This increases the likelihood of widespread systemic absorption, typically associated with a greater risk of sexual and other 

In this article, we get acquainted with the anatomy of the scalp and shed light on how different topical formulations interact with the layers within it. Keep reading for an up-close and personal look at your scalp.

The outermost covering of your scalp, the skin surrounding your cranium typically measures between 

. In addition to acting as a physical barrier, the skin of the scalp has several other functions including temperature regulation, hormone production, UV light filtration and moisture regulation (

The scalp skin contains 2 distinct layers, each made up of several different cellular membranes: the 

The connective tissue layer is made up of 

 (fat molecules) and fibers bound together in one membrane. It’s attached to both levels of the scalp skin – all three move as one unit (Germann et al. 2021).

-skin) this protective layer insulates the skull. The thickness of the lipid layer varies at different points on the body and differs in relation to body fat percentage, to a degree. Its function remains the same, regardless of thickness: subcutaneous fat buffers external force and protects bone, tissue and important functional components within these deeper layers. 

The scalp doesn’t contain a layer of muscle tissue; it’s “all brain, no brawn”. The 

) is an intermediate connective membrane that exists in place of striated muscle tissue. This dense sheath is sandwiched between the subcutaneous (

 skin) connective tissue and the loose areolar connective tissue beyond. 

Primarily composed of the protein collagen, the aponeurosis is loosely striated and visibly fibrous. Similar to ligaments and tendons found throughout the body, its structure borders elasticity and total rigidity. There are no blood vessels or nerves embedded within the connective tissue layer; absorption cannot occur within this level of tissue at the scalp.

From a functional standpoint, there is no need for a high degree of mobility at the crown of the head. The aponeurosis acts as a passive structural element, holding layers above and below it together. This membranous layer generally follows the shape of your natural hairline, extending across the crown of the head and connecting several 

 muscles that exist apart from the scalp (

 beneath it. This layer is more fluid than both the dense connective tissue layer and the aponeurosis, allowing for lateral movement in response to traction and shifting between the layers above and below.

 tissue. This same kind of thin membrane encases all of the bones in your body (

The pericranium contains blood vessels that support cell synthesis within the scalp. It consists of 2 layers:

 layer, which contains fibroblasts that manufacture collagen and other cellular structural elements

 layer, which contains cells that aid in the development of bone tissue

The pericranium is the final layer of tissue before you reach the bone of the skull. 


 at the scalp can negatively impact sebaceous and sweat glands, hair follicle health and normal hair growth (Makrantonaki et al. 2011). Increased scalp DHT is a leading cause of hair loss in men; it causes the 

Hair follicles can become miniaturized as a result of elevated DHT within the scalp. These damaged follicles typically produce shorter 

 hairs anchored in the more superficial papillary dermis. Hairs embedded in this dermal layer don’t extend far enough into body to really benefit from nutrient-rich, oxygenated blood transported by blood vessels in deeper tissue layers.

 is produced within the dermis, the deeper layer of the scalp skin. Topical drugs like finasteride and dutasteride have to reach the dermis to effectively target hair loss. 

 necessary. Transported further away from the scalp and towards the bloodstream, these drugs can negatively impact DHT levels throughout the body. 

Once they have entered systemic circulation via blood vessels within the scalp, 

 carry a greater potential risk of side effects including s

Choosing a topical medicine to treat your hair loss becomes easier when you understand scalp anatomy. Taking time to consider how medications like topical finasteride interact with each of the scalp’s layers is an important part of your hair growth journey that can help inform your decision.


The epidermis acts as a protective barrier to an expansive network of blood vessels, tissue, nerves and bone beneath. While the thickness of this layer varies at different points across the body, it is only about 1.5mm thick at the scalp.

This level of scalp skin contains 5 distinct cellular layers: the 

The stratum corneum is the outermost cellular level, spanning the surface of the skin. It’s made up of cells called 

 — the same type of cells that form the hair shaft (

). The stratum basale is the innermost membrane within the epidermis. It separates the more central cellular levels from the dermis beneath.

The dermis is the thicker of the two layers of skin, typically measuring between 2-4mm (

). While it contains fewer distinct layers, it houses more functional elements than the epidermis. Among these are various glands, nerves, connective tissue, blood vessels and hair follicles. 

(DHT) — the androgen associated with AGA — is also produced within this specific layer of skin.

The dermis can be separated into two general levels, each housing different components: the 

 lies directly beneath the epidermis. It contains sweat, sebaceous and endocrine glands, as well as a complex network of small blood vessels called capillaries that supply oxygenated blood to the scalp skin and hair follicles (Brown and Krishnamurthy 2021).

 is the more visceral dermal layer, found alongside the 

. It’s made up of mostly collagen and elastin. These two cell types lend themselves to skin elasticity and make this layer more dense than the papillary dermis (Brown and Krishnamurthy 2021). 

Normally, healthy terminal hairs sprout from follicles rooted in this deeper dermal layer, extending into the subcutaneous tissue beneath.

The subcutaneous connective tissue contains a higher density of blood vessels than the dermis, which aids in 

. Healthy hair follicles that extend into this layer receive nutrients from arteries carrying oxygenated blood away from the heart, allowing terminal hairs to become longer and reach maturity.

 carrying oxygenated, nutrient-rich blood to the scalp are found within the dense connective tissue layer (Germann et al. 2021):

 is one major outbound blood vessel found within this layer. This vein circulates blood from the scalp back towards the heart, travelling through a network of smaller blood vessels within the more peripheral loose areolar connective tissue layer beneath the aponeurosis.

Other noteworthy veins that move blood away from the scalp include (Germann et al. 2021):

The dense connective tissue layer also contains lymphatic vessels that maintain immune function within the scalp. The parotid, cervical, submandibular, occipital and mastoid lymph nodes are found within this level, circulating cellular fluids containing lipids, immune cells and cellular waste away from the scalp (Tajran and Gosman 2021).

A series of three muscles found just above the ears:

(located at the front of the head, spanning the forehead) 

(found at the nape of the neck, extending across the base of the head)

This loose tissue layer contains a complex network of tiny 

 veins. These circulatory pathways connect the dense connective tissue layer to complex clusters of blood vessels deep within the skull, called 

. Deoxygenated blood is distributed to different venous sinuses via emissary veins. This 'used' blood is then circulated throughout the body, and eventually makes its way back to the heart (Germann et al. 2021).

The loose areolar tissue layer is often referred to as the ‘

’ of the scalp. Blood vessels embedded within this level of the scalp are typically smaller than those found within more superficial layers. 

Bacterial infections, topical medications and any other foreign substances that enter the bloodstream via the loose areolar connective tissue layer are more likely to pose a serious threat to brain health and the body's overall function.

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