What Are the Reasons for Sudden Hair Loss?

Medically approved by
Dr Earim Chaudry
Last updated
7th January 2022

In 30 seconds…

Male pattern baldness (androgenetic alopecia), the most common cause of hair loss for men, usually develops gradually over many years.

But hair loss can sometimes occur suddenly, often as the result of an underlying health condition, poor diet, or even stress. This might feel alarming at the time, but in many cases your hair will regrow naturally once your health improves. 

Hair loss is a fact of life. We all lose between 50 and 100 hairs per day, as a normal part of our hair growth cycle. As your hair follicles enter the Telogen (or resting) phase of growth, the old hair shaft in each follicle is released and the cycle can begin again by producing a new hair. 

However, sometimes the growth cycle can be disrupted and you can find yourself suddenly losing more hair than usual. This may be an overall thinning on your scalp, bald patches appearing, or – in severe cases – the loss of all hair on your head. 

In this article, we review the causes of sudden hair loss and how they can be treated.

Anagen Effluvium

The longest phase of your hair growth cycle is the Anagen phase. This is the growth phase, where individual hairs grow at a rate of 1 to 2 cm per month, and it usually lasts 2 to 7 years. Normally, 80 to 85% of your hair follicles will be in the Anagen phase at any one time.

Anagen Effluvium is a condition where large amounts of hair are lost rapidly, despite the hair follicles being in the Anagen phase. Hair loss may occur on the scalp and on other parts of the body. For some people, all the hair on their scalp may fall out.

A number of medical conditions may be responsible for Anagen Effluvium. In particular, it is one of the side effects of chemotherapy or radiotherapy treatment for cancer. However, it can also be caused by a chronic infection or by malnutrition. For example, if you have iron deficiency anaemia then that could cause this type of hair loss.

The good news is that with Anagen Effluvium hair growth usually resumes spontaneously once the underlying cause has been treated. With chemotherapy, hair typically grows back 3 to 6 months after stopping treatment.  

Telogen Effluvium

One of the most common causes of sudden hair loss is Telogen Effluvium. As discussed above, the Telogen phase of the hair growth cycle is where hair shedding naturally takes place: an old hair is released from the hair follicle to make way for a new hair. This phase lasts around 100 days.

Usually, only 10% of your scalp hair follicles are in the Telogen phase at one time, but when you experience Telogen Effluvium this can increase to 30% or more – leading to increased hair loss across your scalp. You might see more hair falling out onto your pillow, in the shower, or on your comb. Your hair may look thinner but it’s rare to see large bald spots.

Telogen Effluvium is typically caused by the body suffering major stress of some kind, and hair loss takes place suddenly 2 or 3 months after the traumatic event. Causes include major surgery, a serious infection, an illness such as thyroid disease, a sudden change in diet, weight loss, severe psychological stress, or medications such as beta blockers and antidepressants.  

If you’re experiencing Telogen Effluvium, it’s likely that you will see your hair grow back naturally over the next few months.

Alopecia Areata

If you’ve spotted an unusual bald patch, or several bald patches, that have suddenly appeared on your scalp, these could be the result of a condition called Alopecia Areata. This is an autoimmune disease where your immune system attacks healthy hair follicles and causes your hair to fall out.

Alopecia Areata normally only causes small bald spots, but in rare cases it can result in total hair loss, or Alopecia Totalis.

Available treatments for Alopecia Areata include corticosteroid creams applied topically to the affected area or injected, anthralin cream, and oral immunosuppressants. However, some people will find their hair grows back on its own over time. 

Tinea Capitis

Sudden patchy hair loss accompanied by an itchy, flaky scalp may be caused by Tinea Capitis – a ringworm infection of the scalp. It’s treatable with anti-fungal medication for 6 to 12 weeks, but hair can be slow to regrow.

You can help prevent Tinea Capitis by avoiding sharing hats, combs or hairbrushes with anyone else, to make it less likely you will pick up an infection.

Other Causes of Hair Loss

If you find you’re losing hair more gradually, it could be that you’re experiencing one of the following types of hair loss: 

Male Pattern Baldness (Androgenetic Alopecia)

For 90% of men, the cause of their hair loss will be Androgenetic Alopecia, otherwise known as male pattern baldness (MPB). In contrast to the conditions discussed above, MPB usually progresses gradually and hair is lost in a certain pattern – starting with a receding hairline and then a bald spot at the crown. MPB can begin at any time, even as young as your teenage years.

It’s a form of hereditary hair loss, meaning whether or not you experience it will be strongly influenced by your family history. MPB occurs when your hair follicles are weakened by the activity of an androgen (male sex hormone) called DHT. DHT is produced from testosterone (another of your male hormones) by an enzyme named 5ɑ-Reductase. As you age, more DHT is produced, more of your hair follicles are weakened, and more hair loss results.

One of the best treatments for MPB is the oral medication, Finasteride (also called Propecia), which blocks 5ɑ-Reductase from producing DHT. Another effective option is topical Minoxidil (Regaine or Rogaine), which helps increase blood flow to the scalp for rejuvenated hair follicles.

Traction Alopecia

Another form of hair loss that can develop gradually is Traction Alopecia (sometimes called Traumatic Alopecia). This occurs when strain is placed upon individual hairs for a long period of time, causing breakage at the level of the scalp and damage to hair follicles.

Traction Alopecia can be caused by hairstyles such as pony tails, man buns, and cornrows – anything that involves styling the hair by pulling it tightly. Wearing a tight cycling or work helmet on a regular basis could also put strain on your hair.

In addition, pulling at your own hair or beard – whether absent-mindedly or because of the psychological condition Trichotillomania – can cause Traction Alopecia.

You can help prevent this type of hair loss by choosing a looser hairstyle, or, in the case of Trichotillomania, you can try a course of Cognitive Behavioural Therapy (CBT) which may help to reverse the hair-pulling habit.

Key Takeaways…

Sudden hair loss is often the side effect of another medical condition or treatment, and in many cases it should grow back naturally, once you have recovered from your illness. 

However, it’s still important to seek medical advice if you experience sudden hair loss. You may have an infection that needs to be treated. Alternatively, your doctor may be able to adjust existing medication if that is responsible for your loss of hair.

The state of your scalp can be an important indicator of the state of your health, so don’t simply shrug off thinning hair or balding as “just one of those things”. It may be a sign that you need to change your diet or reduce stress in your life – make sure you look after yourself.

Effective in over 9/10 men, our hair treatments are clinically proven to help you keep and grow your hair.

While we've ensured that everything you read on the Health Centre is medically reviewed and approved, information presented here is not intended to be a substitute for professional medical advice, diagnosis, or treatment. It should never be relied upon for specific medical advice. If you have any questions or concerns, please talk to your doctor.

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