The main causes for hair loss in both women and men | Ask Doctor Anne


A few weeks ago I had a nightmare in which I suddenly lost all my hair, it just started to fall out in huge patches and I remember waking up in full panic, instantly checking my head.


Woman looking frightened touching her hair.
Losing your hair? Here is what might be the cause.


It was just a nightmare, but it made me think about the different causes for losing your hair, both in men and in women, because against common misconception, hair loss is not restricted to those born male.

So if you had a similar nightmare, or if you just feel you are shedding more than usual and want to know what the reason could be, here is the blog post for you.



The physiology of hair growth and hair loss

It is normal to lose around 100 hairs a day on average, meaning that some people lose less and others, like me, more than that. Every person has their own, personal base line of hair loss that is considered their normal.

To understand why that is, we need to understand how hair grows: It comes from the hair follicle and starts growing from the hair bulb, which then through the hair isthmus leaves the scalp and protrudes as hair shaft.

As long as the hair is in the so-called anagen phase, it keeps growing from the hair bulb, meaning the shaft is pushed further and further and so the hair gets longer and longer. This anagen phase can last anything between 2 to 6 years – the explanation why people can grow their hair to different lengths – and on average 85 to 90 % of your hair are in this phase.

After this growth phase comes the catagen or regression phase in which growth slows down until it enters the telogen phase, in which the complete hair including hair bulb falls out. This takes around 3 months, meaning that after it has stopped growing, your hair stays on your head for around that long until it sheds and the cycle starts anew.
As this is only around 15% of the hair on your head and does not happen in patches, you don’t really notice the shedding and regrowth on your head.


Picture of the anatomical model of a hair
Picture of the anatomical model of a hair


Hair breaking and hair shedding

Strictly speaking hair loss is just the shedding of hair with the hair bulb included by hair that has entered the telogen phase, so losing the whole hair. The loss of volume many notice though can also be caused by hair breaking off at the shaft – the hair is still in the follicle and growing, but due to structural changes it breaks off at the shaft so it appears much shorter than it should actually be given its age, and if that happens a lot, can give the appearance of you having less hair, similar to when you shed more than usual.
For that reason hair shaft issues with hair breakage are often included in the causes for hair loss alongside the ones that affect the hair follicle.

No matter what the cause for your hair loss is though, taking care of your hair’s health to avoid breakage is always among the recommended steps to take. (More info: What is Olaplex and how does it work)


Is this hair loss or hair breakage?
Image by Martin Slavoljubovski from Pixabay


What are the main causes of hair loss?

Leaving hair breakage aside, hair loss (the medical term is alopecia) exceeding the normal amount is usually caused by changes in the hair follicle and can be divided into scarring and non-scarring hair loss. Now it isn’t actual visible scars that is referring to, although that would be entirely possible, there are no hairs growing once the tissue is destroyed, but rather to the fact if the hair follicle is damaged irreversibly or not.

So scarring hair loss, which is very rare, means that the follicle is destroyed with no chance for regrowth, while non-scarring hair loss, the more common form, means that regrowth is possible. Non-scarring hair loss that is left untreated can turn into scarring hair loss over time, when the follicle gets irreversibly damaged, so it is always a good idea to seek out the cause early and start treatment as soon as you realize something is off.

Which can be kind of late, we do have on average 100.000 hairs on our head and when the thinning gets noticeable, usually around half of them are already gone.


Here now a (surely incomplete) list of the main causes of hair loss that I will explain more in depth below:

  • Male or female pattern hair loss or androgenetic alopecia
  • Alopecia areata
  • Telogen effluvium
  • Traction alopecia
  • Alopecia due to local or systemic infections
  • Alopecia due to autoimmune diseases
  • Alopecia due to allergies
  • Alopecia due to nutritional deficits
  • Hair loss triggered by medication
  • Trichotillomania


Male pattern hair loss – what we usually think of
Image by kalhh from Pixabay


Androgenetic Alopecia or male/ female pattern hair loss

Androgens are hormones and the term androgenetic already gives away that this form of hair loss depends on both the hormones and the genes. Androgens are sex hormones like testosterone (which is present in people of both sexes, just usually in different concentrations) and when this testosterone is bound to 5-Alpha-Reductase that conveniently sits in the hair follicle among other places, gets transformed to Dihydrotestosterone (DHT), which is more potent and also both reduces the length of the anagen phase so the hair falls out quicker and over time minimizes the hair follicle so it stops growing new hair.

The density of 5-Alpha-Reductase is highest on the top of the head, which is why people born male usually lose their hair via a receding hairline and a bald spot on the brown of the head that slowly move towards each other, so called male-pattern hair loss, and people with a uterus via thinning starting at the middle part and spreading outwards from there, so called female-pattern hair loss. This is not age related and can happen as early as in your 20s, but chances of it becoming visible increase with age, which is why we usually associate it with getting old.

Your genetic predisposition determines the amount of 5-Alpha-Reductase and the hair follicles susceptibility to DHT, so some people will grow old with a full head of hair and others won’t – that is the genetic part in androgenetic alopecia.


Alopecia areata and other autoimmune diseases

If your hair doesn’t fall out in the typical male or female pattern, but instead suddenly in a round spot with skin that is perfectly fine and smooth underneath, you most likely experience Alopecia areata, an autoimmune condition where your body perceives the hair follicle as foreign and starts attacking and destroying them. That can happen both on the head only or on the body only or affect both. It can also rapidly spread to the entire head , meaning you don’t only use your hair in patches, but your hair falls out everywhere. When treated early, it is usually reversible.

There are other variations of autoimmune diseases that cause hair loss via the same principle, but that usually affect other structures of the body as well, like systemic lupus erythematosus or discoid lupus, which only affects skin and hair, but leads to red, inflamed patches on the scalp and not the smooth skin alopecia areata has.

Any condition that comes with chronic inflammation, like psoriasis for example, can also lead to hair loss in the affected areas.


Telogen effluvium

Opposed to the conditions mentioned earlier, Telogen effluvium is a diffuse form of hair loss, meaning you lose hair not in a certain pattern or spot, but rather everywhere, so your hair gets gradually thinner over time.

The reason for this is usually a stressful event your body went through that shifted more hair than usually from the anagen in the telogen phase, hence the name. As the time between shifting from anagen over catagen to telogen and the hair actually falling out is around three months, it can be hard linking the stressful event to the start of the hair loss three months later.

Stressful events can be both physical stress as in an operation, a systemic infection (the reason why many people experience hair loss after COVID-19), crash dieting, extreme sports like running a marathon or giving birth (although there are more reasons for postpartum hair loss) and psychological stress like losing someone close to you, stress at the workplace, moving, losing your job, financial insecurity, abuse, whatever comes to mind here.

As in this case the follicle isn’t damaged, the hair will eventually grow back and the length of the hair cycle return to normal, so it is reversible. Unless of course the stress is ongoing – if that is the case, you can experience chronic telogen effluvium which, silver linings, will make your hair thin, but will not cause baldness.


Beautiful dancers with tight hair styles
Beautiful dancers with tight hair styles
Image by Evgen Rom from Pixabay


Traction alopecia

Traction alopecia is a special form of hair loss that is self.made by wearing hair styles that are so tight they constantly pull at the hair follicle, damaging it over time. It is most common in people that wear really tight braided hair styles or in people dancing ballet required to wear a really tight bun that pulls the hair back.

The hair loss appears where the traction takes place, so usually at the front hairline, which starts receding, but depending on the style of braids you have could also affect the center part or the sides.


Alopecia due to systemic infections, allergies or nutritional deficiencies

Hair loss, usually not in a specific pattern but more diffuse, can be a side effect of many other things like systemic infections with general inflammation and high fever, but also due to allergic reactions to products like shampoo or hair dye applied to your scalp and, last but not least, due to nutritional deficiencies.

Now I often hear the question “What lack of Vitamin causes hair loss?” and it isn’t something you can say exactly. A lot of nutrients affect hair growth and hair structure, so will affect shedding and breakage, and the more common ones are protein, Zinc, Iron, Folic Acid as well as Vitamin D and Vitamin B 12.

Side note here: Do not take prenatals or Biotin hoping it will improve your hair – unless you are deficient, it will not have any effect.


Alopecia triggered by medication

Hair loss is a possible side effect of many medications, the best known one being some of the ones used for chemotherapy. Others where this is a potential side effect are anticoagulants, some antidepressants and also Roaccutane, the oral acne medication.

The latter is probably the source of the myth that retinol can make our hair fall out – it won’t when applied topically.



Trichotillomania is a psychological disorder where the person affected compulsively pulls out their hair – either on the head only or also in the form of lashes and/ or eyebrow hair.

Over time that can lead to growing bald spots in the area most affected, and similar to repeatedly waxing or epilating an area, can reduce the amount of possible hair growth due to damage done to the hair follicle.


Why am I suddenly losing so much hair and how can I stop my hair loss?

As you can see, there are a variety of different causes for hair loss in men and women and it isn’t always easy to determine what causes yours.

My suggestion would be to first see if it is hair shedding you are experiencing or hair breakage – you can determine that by looking at the hair you are losing to see if it has the bulb attached or not. If you can see the bulb, it is hair shedding, if there is no bulb, it has been breaking off.

Then look for the pattern you are losing your hair – is it all over as in telogen effluvium, only at the crown of the head or quickly in one round spot with smooth skin? Note down any other symptoms you might be experiencing, think about any new things you used on your hair that could have triggered an allergic reaction, take a look at your diet, your lifestyle and your stress levels during the last six months.

And when you have gathered all this information, go see a doctor about it if the hair loss bothers you.
Seeing the doctor means you’ll get confirmation on the underlying cause and treatment specifically tailored to your needs. After that patience is required, as even once the hair loss is stopped, the regrowth will take quite some time.



Hair loss in both people born male or female can have a variety of causes, including changes in the hair growth cycle and the hair follicle through systemic disease, autoimmune conditions, medication, hormonal or lifestyle induced factors. Most types of hair loss are reversible when treated correctly, but this treatment will require patience.
The main things you notice are an increase in hair shedding compared to your usual baseline of hairs lost and hair thinning, which only occurs when you have already lost around half of the hair you usually have.
Depending on the underlying cause, the pattern in which you are losing your hair can vary. Unless you are nutrient deficient, taking a supplement will not help with your hair, so your best approach is gathering all the information available to you and see a doctor, preferably a dermatologist, about it.


The main causes for hair loss in men and women
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