Which Illnesses Can Cause Hair Loss? Common Medical Causes Explained

Key Takeaways:

1. Is hair loss always caused by illness?  No, not always. Hair loss is commonly caused by factors other than illness, they can be part of natural body changes, and some hair shedding is part of the normal hair cycle.
   
2. Which illnesses can cause hair loss?  When we are ill with certain conditions, they can put our body under strain, it can disrupt the normal hair cycle and ultimately manifest as hair loss. These conditions include thyroid disorders, iron-deficiency anaemia, autoimmune conditions, hormonal disorders and scalp infections.
   
3. Can the pattern of hair loss reveal the cause?  Yes, however, it can be ineffective in determining the cause of hair loss if taken on its own. The pattern of hair loss can provide useful clues as to the underlying cause. For example, distinguishing between whether you have diffuse shedding, smooth bald patches, broken hairs, or an inflamed scalp can narrow down suspected causes. This is even more relevant when it is combined with symptoms you may have elsewhere in your body.
   
   
4. How are illness-related hair loss conditions diagnosed? A GP or dermatologist will likely ask you about your relevant medical history, examine your scalp, arrange for blood testing if they need to check a relevant deficiency, and occasionally might take a sample of skin from your scalp (called a biopsy)
   
5. Should you consider a hair transplant straight away? No. If you are ill, the priority is to get yourself better first. You should not consider any surgical options until the underlying condition is diagnosed and treated. Hair transplantation is an elective surgery and should only be considered after you have fully recovered and have met the right criteria to be fit for surgery.

In this article, we explore which illnesses can cause hair loss, what are the signs to look out for, and the next best steps to take to look after your health and your hair.

What is illness-related hair loss?

Illness-related hair loss is when you have a medical condition which disturbs natural hair growth, inflames the scalp, or damages the hair follicle; these contribute to hair loss  

Hair growth is a process that occurs in cycles. Most of your scalp follicles are actively growing; a small amount of them are resting and ready to release older hairs before new ones can emerge. On average, around 100 hairs fall out of your scalp each day.¹

What illnesses can cause hair loss?

Each cause of hair loss that is attributed to a specific illness will present with its own pattern. Here is a list of illness-related hair loss causes:

Thyroid disorders

Having a disorder of the thyroid, such as an underactive or overactive thyroid, can affect the hair. In both of these conditions, it is common to see more widespread, generalised hair shedding, leading to thinning of the hair or a reduction in volume rather than any concentrated bald patches.²

With an underactive thyroid, you may feel unusually tired or cold, gain weight, and notice your skin is drier than usual. If you are a woman, you may notice your periods are heavier or less predictable than normal.

An overactive thyroid will make you feel hotter than it actually is. It can also manifest with symptoms such as trembling, heart palpitations, weight loss, and hair thinning. 

Iron-deficiency anaemia

Low iron can be linked to an increase in hair shedding and diffuse thinning. Signs that you have low iron include tiredness, pale skin, headaches, breathlessness, brittle nails or unusual cravings.

In order to investigate an iron deficiency, you will need to have a blood test. Although iron deficiency can be nutritional in nature, do not take high-dose iron ‘just in case’; it is important that you are diagnosed by a doctor who can also look at the underlying cause of low iron, which may be serious and should not be ignored.³

Autoimmune conditions

Certain autoimmune conditions may inflame the hair follicles and lead to hair falling out. In autoimmune conditions, your body mistakenly targets your own healthy cells for destruction.

An example of this is alopecia areata. It is the most common example of an autoimmune condition resulting in hair loss. The immune system ends up targeting the hair follicles and usually produces smooth, round patches of hair loss.⁴

Lupus is another autoimmune condition that can lead to hair loss by the appearance of inflammatory rashes on the scalp. Alongside the scalp symptoms with autoimmune conditions, you may also experience joint pain, tiredness, and changes to your nail appearance.^5,6

Hormonal conditions

Polycystic ovary syndrome (PCOS), now renamed polyendocrine metabolic ovarian syndrome (PMOS), may be associated with thinning of the central hair parting and crown. Some other symptoms can include increased facial and body hair.⁷

Female pattern hair loss is common and does not mean that you necessarily have hormone levels that are abnormal. Seek consultation if you have concerns with your hair loss; your GP will decide whether you need further testing or referral.

Scalp infections

There are some infections in which the scalp can be damaged, resulting in hair loss. Tinea capitis, or scalp ringworm, is a fungal infection that causes itchy or scaly patches on the scalp, broken hairs, redness or crusting. 

The treatment is quite straightforward. You will need to apply antifungal medication to the scalp. Early initiation of the appropriate treatment is important to avoid intense inflammation and possibly the scarring of hair follicles.⁸

Inflammatory and scarring scalp conditions

Lichen planopilaris, frontal fibrosing alopecia, central centrifugal cicatricial alopecia and discoid lupus can all lead to the destruction of hair follicles through direct inflammation.^9,10,11

The warning signs that these conditions are damaging future hair regrowth include: a burning sensation on the scalp, pain, tenderness, redness, scale, a receding frontal hairline, or smooth, shiny areas of hair loss.

Left unattended, these conditions tend to spread over time, and the follicles already affected are unlikely to recover their ability to make hair. Getting an early dermatology assessment is crucial in these cases to offer you the best chance of controlling inflammation and protecting the hair that remains.

Severe or prolonged illness

A generalised illness or a high stress condition on the body, such as a high fever, severe infection, operation, or emotional causes, can cause shedding across the scalp, often with the hair shedding coming months after the initial trigger.¹²

‘During consultation, any active hair loss condition must be investigated and diagnosed prior to considering any hair transplant, especially in cases where there is suspected scarring hair loss. This is particularly important in such cases as hair transplant surgery could fail if transplanted into an area of active scarring alopecia.”

Dr Roshan vara, Co-Founder and Surgeon at The Treatment Rooms London

How do illnesses cause hair loss?

You may be wondering how it is that such different illnesses can all affect hair growth. There are a few ways that this can happen:

Disruption of the hair cycle

Illness, surgery, or intense physical or emotional stress can all push more than the usual amount of follicles to enter into a resting phase. Once in the resting phase, the hair will start to shed; the result is a delayed onset of a diffuse shedding of hair, which takes place 3-6 months after the initial cause.¹²

Immune-system activity

In autoimmune diseases, the body misidentifies normal healthy cells as foreign bodies and mounts an attack on these useful and productive cells, thereby altering normal cellular processes.

When you have alopecia areata or certain forms of lupus, the hair follicle becomes inflamed, and the hair is shed. In alopecia areata, the inflammation is usually non-scarring, but with Lupus it can be either scarring or non-scarring.^4,5

Hormonal or nutritional disruption

Thyroid hormone imbalance, hormonal conditions where you end up producing more androgens, as well as iron and other nutrient deficiencies can all end up disturbing normal follicle activity. 

Direct inflammation and follicle damage

Infection or inflammatory scalp disease can injure hair follicles and weaken hair. Once scar tissue replaces a follicle, regrowth of hair is no longer possible from that site.^8,9,10 

What signs and symptoms should you look for?

You can use the appearance, pattern, distribution, and timing of the hair loss as a guide when to seek an assessment. It is not intended for you to diagnose yourself; that is best left to a medical professional. Look out for the following signs:

1. All-over shedding: This may follow illness or surgery, or accompany iron or thyroid problems.
   
2. Smooth bald patches: These are a common feature of alopecia areata, a type of autoimmune hair loss.
   
3. Scale with broken hairs: This raises the possibility of a fungal scalp infection, like tinea capitis.
   
4. Pain, burning, pus-filled lump or shiny skin: These signs can indicate an active inflammatory process or scarring and require a timely medical review to prevent progression and potential permanent scarring and hair loss.
   
5. Symptoms beyond the scalp: Such as fatigue, breathlessness, weight changes, temperature sensitivity, altered periods, joint pain, or rashes are always worth mentioning to your doctor if you notice them alongside your hair loss
   
6. Delayed shedding: When your loss starts a few months after a trigger such as an illness or operation, then the picture of hair loss matches that of stress shedding (telogen effluvium)

Could an illness be causing your hair loss?

As discussed in the article, it is possible that an illness may be causing your hair loss, but many causes can present similarly, or more than one can be occurring at the same time.  Arrange an assessment by a GP or dermatologist if the loss is sudden, unexplained, persistent or distressing, or if your scalp is painful, inflamed, scaly or shiny. 

An assessment may include elements of the following:¹³

• A history of the timing, recent illness, medicines, diet, menstrual changes and family hair patterns
  
• Examination of the scalp, distribution of hair and presence of hair breakage
  
• Targeted blood tests, which can include a full blood count, iron levels and thyroid function.
  
• A biopsy of the scalp to examine it more clearly under a microscope

Most of the time, the diagnosis can be made through the appearance, pattern, distribution, and history of hair loss.

Blood testing is not always required;  it is not necessary in common cases such as pattern hair loss, or in other cases, such as alopecia areata and other scarring disorders, it can be considered if there is suspicion of an underlying medical condition causing the hair loss.

How is illness-related hair loss treated?

Treat the underlying condition

If it is established that you have an underlying illness that is causing your hair loss, then naturally, the first step to take is to treat the underlying illness in order to prevent further hair loss and in some cases, reverse the hair loss experienced.

For example, you may take thyroid medicine for confirmed thyroid disease, iron replacement for a proven deficiency, antifungal treatment for tinea capitis, and specialist anti-inflammatory medications or immune-modifying treatments for autoimmune or scarring hair loss conditions. 

If you have polyendocrine metabolic ovarian syndrome or PMOS (Formerly called PCOS), then the management will be tailored to your symptoms, health risks, and future pregnancy plans.¹⁴

Allow time for recovery

Hair responds slowly to treatment, and this can be discouraging to some patients. It may feel as though you are still losing hair and treatment is not working, but this is usually because hairs that have been placed in a resting state take around 3 months before they complete their cycle and shed.

This can account for ongoing excessive hair shedding you may see during treatment. 

Support the hair and scalp

It is important for you to get things right to keep your recovery on track. There are some simple but important ways of keeping your care straightforward.

Make sure you eat a balanced diet, supplement deficiencies that have been diagnosed, and limit tight hairstyles, harsh chemicals, and excessive heat. These steps help reduce avoidable breakage, which will only further compound your hair loss. 

There are also certain hair-loss medications you can use to help prevent further hair thinning or help prolong the amount of time hair follicles remain in the active phase of growth. These will be prescribed by a doctor if they feel you will benefit from them.

Hair transplants and illness-related hair loss

A transplant moves healthy hair follicles from one part of your scalp to another; it does not treat the illness that caused the hair loss. Surgery is not advisable if you have temporary shedding, your diagnosis is not settled upon, or if inflammation remains active.¹⁵

If you have a scarring form of hair loss, hair transplantation may only be performed once the condition is managed and has been stable for some time. The reason for this is because grafts may not survive as well in skin that has ongoing current inflammation. In addition, implanting new hair in areas of past inflammation, can sometimes reactivate it, which will end up also causing the transplanted hair to also fall out. 

If you have a scarring form of hair loss and are considering a hair transplant, you will almost certainly need to be assessed by both a dermatologist and an experienced hair transplant surgeon first.^15,16

“In our clinic we see many patients with previous scarring alopecia. These conditions must be stable before planning a hair transplant. If they have current active shedding and inflammation, surgery risks failing entirely. We recommend being assessed by a Dermatologist with a biopsy taken to ensure the condition is stable and not active before proceeding with plans for a hair transplant. This extra diligence and wait can be heartbreaking for some of our patients who are looking for a quick solution for their hair loss, but the advice is given for the safety and best interests of our patients.” 

Dr Roshan Vara, Co-Founder and Hair Transplant Surgeon at The Treatment Rooms London

If not an illness, what else could it be?

If your hair loss is not caused by illness, then common other causes can include

• Male or female pattern hair loss
  
• Excessive tension on the hair roots by hairstyles or headwear 
  
• Compulsive hair pulling disorder (trichotillomania)
  
• Pregnancy or menopause related
  
• Rapid weight loss
  
• Psychological stress
  
• Hair breakage

These can overlap with illness; for example, shedding hair may reveal an already developing male or female pattern hair loss. That is why it is so important to contact a medical professional to examine your hair and scalp in order to get an accurate diagnosis. 

Conclusion

There are many types of illnesses that can cause increased hair shedding or hair loss. Thyroid disease, iron deficiency, and autoimmune or hormonal disorders can all trigger hair shedding or loss. The pattern the hair falls out in can reveal some telling clues, but ultimately a diagnosis will need an in-person assessment by a doctor. 

Look out for signs of conditions that can potentially cause permanent hair loss, such as sudden, persistent loss of hair or those that come with symptoms such as pain, redness, or a shiny scalp. 

Treating the underlying illness always takes priority, as it is only by taking care of this that we can successfully control any hair loss. Considerations of a hair transplant will be at a much later stage after the acute illness has passed. Depending on the cause of your hair loss and the professional assessment, a hair transplant may or may not be possible.

References

1. NHS. Hair loss [Internet]. [updated 2024 Jan 24; cited 2026 Aug 28]. Available from: https://www.nhs.uk/symptoms/hair-loss/
   
2. British Thyroid Foundation. Hair loss and thyroid disorders [Internet]. Harrogate: British Thyroid Foundation; 2024 May 21 [updated 2024 Jul 4; cited 2026 Aug 28]. Available from: https://www.btf-thyroid.org/hair-loss-and-thyroid-disorders
   
3. NHS. Iron deficiency anaemia [Internet]. [updated 2024 Jan 26; cited 2026 Aug 28]. Available from: https://www.nhs.uk/conditions/iron-deficiency-anaemia/
   
4. British Association of Dermatologists. Alopecia areata [Internet]. London: British Association of Dermatologists; [updated 2024 Apr; cited 2026 Aug 28]. Available from: https://www.bad.org.uk/pils/alopecia-areata
   
5. Concha JSS, Werth VP. Alopecia in lupus erythematosus. Lupus Sci Med. 2018;5(1). doi: 10.1136/lupus-2018-000291.
   
6. British Association of Dermatologists. Discoid lupus erythematosus [Internet]. London: British Association of Dermatologists; [updated 2024 Nov; cited 2026 Aug 28]. Available from: https://www.bad.org.uk/pils/discoid-lupus-erythematosus-dle/
   
7. National Institute for Health and Care Excellence. Polycystic ovary syndrome: diagnosis [Internet]. London: NICE; [cited 2026 Aug 28]. Available from: https://cks.nice.org.uk/topics/polycystic-ovary-syndrome/diagnosis/diagnosis/
   
8. British Association of Dermatologists. Tinea capitis [Internet]. London: British Association of Dermatologists; [updated 2023 May; cited 2026 Aug 28]. Available from: https://www.bad.org.uk/pils/tinea-capitis
   
9. British Association of Dermatologists. Lichen planopilaris [Internet]. London: British Association of Dermatologists; [updated 2022 Nov; cited 2026 Aug 28]. Available from: https://www.bad.org.uk/pils/lichen-planopilaris
   
10. British Association of Dermatologists. Frontal fibrosing alopecia [Internet]. London: British Association of Dermatologists; [updated 2018 Jul; cited 2026 Aug 28]. Available from: https://www.bad.org.uk/pils/frontal-fibrosing-alopecia/
    
11. British Association of Dermatologists. Central centrifugal cicatricial alopecia [Internet]. London: British Association of Dermatologists; [updated 2024 May; cited 2026 Aug 28]. Available from: https://www.bad.org.uk/pils/central-centrifugal-cicatricial-alopecia/
    
12. British Association of Dermatologists. Telogen effluvium [Internet]. London: British Association of Dermatologists; [updated 2025 Oct; cited 2026 Aug 28]. Available from: https://www.bad.org.uk/pils/telogen-effluvium
    
13. Singh S, Muthuvel K. Practical approach to hair loss diagnosis. Indian J Plast Surg. 2021;54(4):399-403. doi: 10.1055/s-0041-1739240.

14. Teede HJ, Tay CT, Laven JJE, Dokras A, Moran LJ, Piltonen TT, et al. Recommendations from the 2023 international evidence-based guideline for the assessment and management of polycystic ovary syndrome. J Clin Endocrinol Metab. 2023;108(10):2447-69. doi: 10.1210/clinem/dgad463.
    
15. True RH. Is every patient of hair loss a candidate for hair transplant? Deciding surgical candidacy in pattern hair loss. Indian J Plast Surg. 2021;54(4):435-40. doi: 10.1055/s-0041-1739247.
    
16. Ekelem C, Pham C, Mesinkovska NA. A systematic review of the outcome of hair transplantation in primary scarring alopecia. Skin Appendage Disord. 2019;5(2):65-71. doi: 10.1159/000492539.