What causes hair loss? Conditions, hormones and medications that can cause it

A small amount of hair loss is completely natural. We can lose anywhere between 50 to 100 hairs a day, without noticing. However, sudden or excessive hair loss can indicate an underlying medical condition.

In this guide, we look at some of the main causes of hair loss.

Jump to:

Scalp conditions that cause hair loss

This section covers the following:

  • Itchy scalp conditions associated with hair loss
  • Scalp infections that can cause hair loss

If you feel you’re suffering from a scalp condition, contact your local GP as soon as possible.

Itchy scalp conditions associated with hair loss

Most people will suffer with an itchy scalp at some point. However, if the itchiness feels constant or painful, you may be suffering from an itchy scalp condition.

The main causes of itchy scalp are:


Dandruff is the result of overactive oil glands on the scalp. Oil in your hair is a natural process regulated by the hormones in your body. However, if it’s overactive, it can irritate your skin and hair follicles.

The main symptoms of dandruff are an itchy, scaly scalp and white flakes of skin falling from your hair and onto your shoulders, which can be embarrassing.

Can dandruff cause hair loss?

Yes, but only temporarily.

This is because dandruff can become so itchy that it inflames the scalp and causes temporary hair loss. There are lots of products available that can help with dandruff—the HSE has a useful page explaining how to treat dandruff. You can also contact your pharmacist or GP for help.

Tinea capitis

Also known as ringworm of the scalp (although it’s not a worm at all), tinea capitis is a fungal infection. It causes circular marks on the skin with flat centres and raised borders, hence the ringworm name.

Common symptoms include:

  • itchy patches on the scalp
  • brittle hair
  • sore scalp
  • swollen lymph nodes
  • low-grade fever


Tinea capitis is highly contagious.

It’s spread from person to person via the sharing of combs, towels, hats or pillows.

If you or your child are suffering, contact a health care professional.

Can tinea capitis cause hair loss?

Yes, in severe cases.

If you don’t get treatment for tinea capitis, the symptoms can get worse. You may develop a kerion, a crusty swelling full of pus. This could leave permanent scarring or bald spots.

Allergic reactions

Allergic reactions to things like hair dyes can cause an itchy, inflamed scalp. If you suffer from sensitive skin, it would be worth avoiding any dye products containing paraphenylendiamine. ISRN dermatology conducted a study and found 1% of their subjects were allergic to paraphenylendiamine.

Many common hair dyes contain this product, so check the ingredients for either paraphenylendiamine, or its abbreviation PPD. Before you use hair dye, always do a small patch test on the back of your ear to make sure you aren’t allergic.

Can allergic reactions cause hair loss?


Because of the wide range of allergies people can suffer from, it’s hard to tell for definite which reactions can cause hair loss. If you suffer from an allergy, it’s best to ask a professional which products you should use, rather than risking it yourself. Severe allergic reactions can cause many problems, hair loss being one of them.

Scalp infections that can cause hair loss


Folliculitis is a common skin condition in which hair follicles become inflamed. It is caused by a bacterial or fungal infection. Anyone can develop folliculitis at any point in their lives.

Symptoms include:

  • clusters of small red bumps or white-headed pimples that develop around hair follicles
  • pus-filled blisters that can break open and crust over
  • a large bump or mass
  • painful skin
  • itchy, burning skin
  • a sore scalp

Folliculitis doesn’t just affect your scalp, but wherever on your body hair follicles can grow.

Can folliculitis cause hair loss?


Often, hair loss caused by folliculitis will be a temporary side effect of the inflamed hair follicles. However, in severe cases with extreme inflammation, hair may permanently fall out.

Lichen planus

Lichen planus is an infection which can affect different parts of your body including your scalp, skin and inside your mouth. Its cause is still unknown. It isn’t infectious and is most likely an autoimmune disease that causes white blood cells to attack healthy skin.

Symptoms include:

  • clusters of shiny, raised, purple-red blotches on your arms, legs and body
  • white patches on your gums, tongue or the insides of your cheeks
  • bald patches appearing on your scalp
  • burning and stinging in your mouth
  • sore patches on your vulva
  • ring-shaped purple or white patches on your penis

(You may only have one or a few of these symptoms.)

Can lichen planus cause hair loss?

Yes, temporarily.

Lichen planus on your skin usually gets better on its own in about six to nine months. Bald patches may appear on your scalp during this time, but they will grow back.

Psoriasis of the scalp

Psoriasis of the scalp can affect parts of your scalp or all of it, causing red patches of thick, silvery-white scales. Some have found psoriasis has caused extreme itchiness, whilst others have suffered with no discomfort.

It can affect many parts of the body, including your chest, arms, legs and scalp.

Can psoriasis of the scalp cause hair loss?

Yes, but only in extreme cases and usually temporarily

Can scalp eczema cause hair loss?


Scalp eczema is a type of atopic eczema, which is the most common form of eczema. It’s usually a chronic condition, although it can get significantly better as you age.

Symptoms include itchy, dry, cracked skin in specific areas of the body.

While it can cause your scalp to become red, sore and sensitive, it won’t cause hair loss.

Diseases that cause sudden hair loss

The following are the main diseases that can cause sudden hair loss in both men and women:

Thyroid disease

Thyroid disease is a broad term that covers diseases that can affect the thyroid gland. These include the following:

Can thyroid disease cause hair loss?


Both hypothyroidism and hyperthyroidism can turn your hair thin and brittle. Severe and prolonged cases of these diseases can cause hair loss. They will affect the whole scalp, giving the appearance of sparse and patchy hair. However, hair will normally return once the disease has been treated successfully.

Thyroid cancer does not cause hair loss itself, but treatments required to combat the cancer can. For more information, see the cancer and hair loss section of this guide.


Alopecia is a disease that can cause hair loss. It can occur in three levels of severity.

  • Alopecia areata—causes hair to fall out in small patches
  • Alopecia totalis—causes all the hair on the scalp to fall out
  • Alopecia universalis—causes the entire body to lose hair

People can experience a mix of all three and so doctors may avoid using these specific terms. People can go through cycles of hair loss and growth due to alopecia. Unfortunately, alopecia has no cure.

What causes alopecia?

Alopecia is an autoimmune disease. This means the disease develops when the immune system mistakes healthy cells for foreign substances such as bacteria or viruses.

With alopecia, the immune system mistakenly attacks hair follicles, causing hair to fall out.

It’s still undetermined what exactly causes alopecia, although it’s generally considered to be related to a person’s genetics.

Stress disorders

Constant stress can cause havoc to your body. High levels of stress kick your hypothalamus into gear and make your body produce stress hormones. These hormones activate your body’s “fight or flight” response, putting your body on high alert so it can sense danger.


Stress can cause a variety of problems, including the following:

  • Headaches
  • Depression
  • Heartburn
  • Insomnia
  • Weakened immune system
  • Higher risk of heart attacks
  • High blood pressure
  • Low sex drive
  • Stomach issues

A recent study found that people with high levels of stress and depression were 48% more likely to die or have a heart attack during the period the study was carried out.

Can stress cause hair loss?


Stress can cause a disorder known as telogen effluvium, which is the thinning or shedding of hair. Emotional or physiological stress disrupts normal hair growth, which in turn causes the disorder.

Hair can grow back once stress levels are back to normal. If you’re feeling constant, high levels of stress, you should speak to your doctor/psychologist to get the support you need.


Iron deficiency anaemia occurs when your body doesn’t have enough iron in its system to produce haemoglobin. It’s often caused by blood loss or pregnancy, so women are at much higher risk of suffering anaemia than men. It can be easily treated by visiting your GP for iron supplements and eating iron-rich foods.


  • Tiredness
  • Shortness of breath
  • Pale skin
  • Heart palpitations
Does being anaemic cause hair loss?

Yes, but it’s rare.

Anaemia can cause hair loss but you’re more likely to suffer from other symptoms first. The hair loss is unlikely to be permanent or severe.

Stomach disorders

The gut absorbs nutrients which then enter the bloodstream. Crohn’s disease, irritable bowel syndrome and other inflammatory diseases cause severe inflammation in the lining of the gut. Not only can the inflammation be painful, it can also cause other issues due to the lack of nutrients.

Symptoms of stomach inflammation disorders

  • Diarrhoea
  • Fever
  • Fatigue
  • Abdominal pain/cramping/bloating
  • Blood in your stool
  • Mouth sores
  • Reduced appetite

Different diseases vary in severity and symptoms. If you have any of these symptoms, contact your GP.

Does Crohn’s disease cause hair loss?


Crohn’s disease and other more severe stomach disorders can cause hair loss. This is because the inflammation can stop essential nutrients entering the gut. Your body needs some of these nutrients to keep a healthy head of hair, so without them hair loss will occur.

The hair loss is unlikely to be permanent, depending on the severity of the disease.

Cancer and hair loss

What types of cancer cause hair loss?

Cancer itself is unlikely to cause hair loss—it’s more the treatments carried out to battle the cancer, the main one being chemotherapy.

Chemotherapy is a scattergun approach to killing cancer, meaning it will blast healthy cells as well as cancer cells. These healthy cells include the ones that make hair follicles.

Do all chemotherapy patients lose their hair?

No. It varies depending on the type of chemotherapy you receive. Some chemotherapies cause your entire body to lose hair. Others may only cause hair loss on the scalp, or may not cause hair loss at all.

Is hair loss from chemotherapy permanent?

No, your hair will grow back after your treatment. This may happen immediately or take a few months. It may look slightly different when growing back—usually a bit darker and curlier—but it’s unlikely to be permanent. Your ‘normal’ hair will usually grow back within six months of stopping the treatments.

Can radiation therapy cause hair loss?

Yes, radiation therapy will generally cause hair loss. However, unlike chemotherapy, it will cause hair loss specifically in the area that is being treated. For example, if you had radiation therapy on your legs, you would only experience hair loss on your legs, nowhere else.

Testosterone and hair loss

Testosterone is a hormone found in all humans. It’s primarily created in the male testicles, but women’s ovaries can make smaller amounts too.

Testosterone is often just associated with the sex drive but it also affects bone and muscle mass, fat storage and blood cell production.

Does testosterone cause hair loss?

There is a myth that bald men have more testosterone and have suffered hair loss as a result. However, this is completely false, and was started in the 1960s when a Yale doctor made some wild claims regarding male testosterone and baldness. It would seem that the link between male pattern baldness and testosterone is more complicated than once thought.  

DHT and hair loss

Having a high level of testosterone will not cause male pattern baldness. Instead, male pattern baldness is likely caused by a reaction between genes and a testosterone by-product known as DHT. Studies have found that DHT found within the scalp is linked to male pattern baldness.

DHT is an important hormone for hair growth in both the scalp and other areas of the body such as chest, arms and legs. A study in 2013 found that blocking DHT can help fight male pattern baldness. However, it should be noted that this is just one study and more will be required to make a definitive case.

How to stop DHT and hair loss

Unfortunately, there is still little evidence that proves there is a way to completely stop DHT. Any shampoos or conditioner products that claim otherwise may be taking their information from false sources.

Medication, supplements and lifestyle choices that can cause hair loss

In this section:

Can zinc deficiency cause hair loss?


Zinc is a mineral that is involved in hundreds of chemical reactions in the human body. For example, it helps creates new cells, heals wounds and process carbohydrates.

Because zinc affects so many systems in the body, having a deficiency can disrupt many bodily functions—hair loss being a major one.

Which foods are high in zinc?

You can purchase supplements to increase your zinc levels, but it is available in a variety of food:

  • Dairy products
  • Meat
  • Seafood
  • Nuts and seeds
  • Beans
  • Peas
  • Lentils

Does beta-alanine cause hair loss?


You can get beta-alanine from foods that contain carnosine, although a lot of athletes take supplements instead. It can cause some side effects such as tingling skin, so it’s worth contacting your doctor before you take supplements. However, there is no scientific evidence to prove that beta-alanine causes hair loss.

Does Nioxin cause hair loss?

There is no evidence, although there are claims it does.

Nioxin is a non-prescription hair loss product. The website for the product says there are no serious side effects, and no studies are available to counter that claim. However, there are claims online from people who, through using Nioxin, have experienced:

  • an itchy, red scalp
  • flaking skin
  • swelling or tenderness
  • dry hair
  • hair loss

These claims are unsubstantiated so take them with a pinch of salt. Just be aware of the potential side effects before trying Nioxin.

Does Topamax cause male hair loss?

It can.

Topamax is the brand name of topiramate, an anticonvulsant drug that helps combat the effects of epilepsy. Unfortunately, like many prescription drugs it can come with a variety of side effects—alopecia being one of them.

For more information about the Topamax and its side effects, visit the National Institute for Health and Care Excellence.

Can finasteride cause hair loss?


Finasteride is another anti hair-loss product, which studies have found can help regrow hair. While several side effects were observed during studies, it was a low percentage of people that actually experienced them. Furthermore, there is no evidence to say that hair loss is one of the side effects.

Does being vegan cause hair loss?

Yes, if you don’t eat the right nutrients.

In an interview by Business Insider, Anabel Kingsley, a trichologist, claimed that nutritional deficiencies caused by veganism can affect hair loss. Key nutrients such as amino acids and iron are mostly found in meat-based products, so careful nutritional planning is needed if you’re to get the right intake of these nutrients.

Vegan-friendly supplements are available. It’s worth talking to your GP/nutritionist about how to get the right vitamins and nutrients in your diet.

Can biotin cause hair loss?

No. It helps with hair growth.

Biotin is a vitamin of the B complex and found in egg yolk, liver and yeast. It’s also an ingredient of health supplements.

Some studies have found that biotin can help increase hair growth. However, due to the complex nature of hair loss and growth, it’s not a miracle cure. Biotin will only help hair loss if you’re biotin-deficient. Surprisingly, biotin deficiency is common among pregnant women. If you’re pregnant and experiencing hair loss, it may be worth purchasing a biotin supplement to combat the condition.


Back to hair loss