Sudden hair loss: the causes checked first

A few weeks ago, everything was fine. This morning, the shower drain is full of hair, so is the brush, and there’s some on the pillow. When hair loss comes on all at once, panic comes with it. Yet sudden hair loss often has a specific cause, and a doctor looks for it in a fairly simple order.

Fast or slow?

The speed is already a clue. Dermatologists at the American Academy of Dermatology (AAD) describe two pictures. On one side, the slow signs: a widening parting, a thinner ponytail, a hairline that recedes a little more each year. On the other, the sudden signs: clumps of hair coming out when you comb or brush, a bald patch or strip that appears within one or two days, or even all (or most) of the hair on your head falling out¹.

Pattern hair loss belongs to the first picture. If you’re in the second, it doesn’t explain everything: something else needs looking for, on its own or on top of it. Here’s what gets checked first.

Look back three months

The most common cause of sudden shedding spread across the whole head is called telogen effluvium. Something disrupts the hair cycle, and lots of hairs switch to their resting phase at the same time before falling out together. Normally 15% of hair is resting; in telogen effluvium, that rises to 30% or more². The shedding starts suddenly, without warning, and is most noticeable after washing or brushing².

The catch is the delay. Hair falls out two to three months after the trigger³, by which point you may have forgotten it. To find the cause, look at your calendar from three months ago. The best-known triggers²:

• giving birth;
• an illness with a high fever, an injury, an operation;
• major stress or a big life change;
• marked weight loss or a very strict diet;
• a new medicine, or stopping a hormone treatment such as the contraceptive pill.

These figures come from a single dermatology clinic in India, and only from women. The causes were identified by asking the patients, so they rely on memory⁴. They give a rough idea, not a rule. The British Association of Dermatologists (BAD) makes the same point about the last bar: for 1 in 3 people with telogen effluvium, no cause can be found².

Testimonials posted on the HairLossTalk forum¹⁰¹¹.

Telogen effluvium usually gets completely better without treatment: the shedding lasts 3 to 6 months, then new hair starts to grow². The details of what grows back and how long it takes are in another article.

Iron and thyroid: the blood test

Two causes can be checked with a simple blood test: a thyroid problem and iron deficiency². Both an underactive and an overactive thyroid can make hair fall out⁶. DermNet also advises checking vitamin B12 and folic acid, and correcting anything abnormal⁶.

Finding the cause changes what happens next. According to the AAD, treating thyroid disease can reverse the hair loss, and hair can regrow once the body gets the nutrients it was missing⁵. On the other hand, telogen effluvium can come back if iron deficiency isn’t treated². There’s more in our articles on iron, vitamin D and B12 deficiencies and on the thyroid and hair.

A normal blood test is an answer too: it rules out two leads and points back towards a past trigger.

Could it be a medicine?

Some medicines have hair loss as a side effect, and starting a new medicine is one of the known triggers of telogen effluvium². If you started something new in the preceding months, note the date and talk to the doctor who prescribed it: they’ll know whether hair loss is a known effect. Above all, don’t stop taking it on your own⁵. Here too, hair usually grows back⁵.

There’s an even faster type: anagen effluvium, where hair is stopped in the middle of its growth phase. It starts suddenly⁹, typically within a few weeks of starting chemotherapy⁵. When a medicine is the cause, hair growth can return to normal within 3 to 6 months of stopping it⁹.

Patches: alopecia areata

If the hair loss doesn’t affect the whole head but forms round, smooth patches, often coin-sized, alopecia areata comes to mind. It comes on suddenly and can also affect the beard, eyebrows or eyelashes⁷. The skin in the patch isn’t inflamed or scaly. Sometimes there’s itching, burning or tingling before or after the hair falls out, and short, tapered hairs called exclamation mark hairs may be seen at the edge⁷.

A doctor usually recognises it on examination, without tests⁷. The follicles aren’t destroyed, and the hair often grows back on its own⁷.

When it’s urgent

Why hurry when the skin is inflamed? Because some types of hair loss, called scarring alopecias, destroy the follicle for good³. Hair lost there doesn’t come back, and treatment is there to slow the disease: it needs to start early⁸. The French Society of Dermatology calls for prompt medical care³.

For everything else, keep this in mind: many of these causes can be treated, and hair often grows back once the cause is dealt with. You just have to find it.

Keep a record from now on

When everything happens fast, memory slips. Three months on, you can’t remember whether the shedding started before or after the fever, or whether your parting already looked like that. Yet that’s exactly what the doctor will ask.

Start the photos now, even if you’re scared of what they’ll show. With Calvap, you take the same photo of your parting, crown and temples every week, following last week’s photo shown as a see-through overlay. Note in the journal the date you start or stop a treatment: that’s often where the trigger hides.

Week after week, you see whether the shedding is slowing down, and whether a patch is spreading or filling in. And at the appointment, you show dated photos instead of searching for words.