Symptoms and Causes of Hair Loss: What to Look Out For

Hair loss is when you lose more hair than normal, or the hair thins in a specific pattern over time. It's worth separating symptoms from causes. Symptoms are what you see and feel: thinning, patches, a receding hairline. Causes are the biological and lifestyle factors driving the loss.

The two are closely linked. In androgenetic alopecia, hair follicles gradually miniaturise, so hair grows back thinner and shorter each cycle. In telogen effluvium, a larger share of hair enters the resting phase after a trigger. In alopecia areata, the immune system attacks hair follicles and creates patches without hair.

This guide first covers what counts as normal shedding, then the typical symptoms and main causes, and finally when to take action.

Hair grows in cycles. Most hairs on the scalp are in a growth phase at any given time, and a smaller share are resting and fall out naturally. That's a normal part of the biological rhythm, not a sign of illness on its own.

Problems arise when this balance is disrupted. If an unusually large share of hair enters the resting phase at once after a trigger, you'll notice increased shedding over the following months. If follicles gradually shrink because of genetics and hormones, hair becomes progressively thinner and shorter, and the change becomes visible as pattern hair loss.

It's the change in pattern or amount over time that separates normal shedding from a genuine hair loss problem. A single heavy day in the shower rarely means much on its own.

Symptoms depend on the underlying cause and can show up as gradual thinning, sudden shedding, well-defined patches, or a changing hairline. Some cases build almost imperceptibly, others develop quickly.

Gradual thinning is very common and especially typical of androgenetic alopecia. You might notice your ponytail feels thinner than before, more scalp showing through in bright light, or hair that generally looks less full. The change happens slowly and is easiest to spot by comparing photos over time.

Patchy hair loss typically shows up as round or oval areas without hair. The skin underneath looks normal — not red, not scarred. This pattern is typical of alopecia areata, where the immune system attacks hair follicles locally and creates sharply defined bald patches.

Sudden hair loss — noticeably more hair in your brush, the drain, or on your pillow over a short period —often points to telogen effluvium. Rather than one specific area thinning, the hair sheds more quickly overall. It typically follows a stressor such as illness, surgery, childbirth, or severe stress.

In men, hereditary hair loss classically shows up as a receding hairline at the temples with thinning at the crown, in a familiar pattern. In women, it more often appears as a wider parting and general thinning across the top of the head, without fully bald patches. The pattern develops gradually over months and years.

Many people notice hair loss in small everyday moments rather than in the mirror — a hairdresser mentioning the hair has thinned, needing an extra twist of the hair tie around a ponytail, or comparing a photo from a year ago with a recent one and seeing a wider parting.

Situations you might recognise:

The experience differs between men and women. Men often notice the hairline first, while women more often describe the hair thinning all over. Both experiences are valid and worth paying attention to.

Normal shedding is part of the hair growth cycle — hairs in the resting phase fall out naturally, and you'll see them in the brush, the drain, or on your clothes, while the hair overall stays stable from month to month.

With true hair loss, that balance is disrupted. You lose noticeably more hair than before over time, and certain areas start to thin. A pattern of patches or a receding hairline can also become clearly visible.

What matters isn't whether there's hair in your brush today — it's whether there's a lasting change in amount or pattern over weeks and months.

A simple comparison:

Hair loss is rarely down to a single factor — several mechanisms and influences often play a role at once.

The main groups of causes:

The first three are the best-documented causes, covered in more depth below.

Androgenetic alopecia is the most common form of hair loss in men and also occurs in women. It's strongly hereditary and linked to hair follicles being especially sensitive to male sex hormones. Over time, follicles gradually miniaturise — hairs grow back thinner and shorter, and some follicles eventually stop producing visible hair altogether. In many men it starts as a receding hairline at the temples with thinning at the crown; women more often notice a wider parting and thinning across the top of the head.

Telogen effluvium occurs when a stressor — illness with fever, surgery, childbirth, severe stress, or significant weight loss — pushes a larger share of hairs into the resting phase at the same time. Normally most hairs are growing and a smaller share are resting; in telogen effluvium that balance shifts, so more hair sheds over the following months. The result is diffuse hair loss without clear patches, and for many people it gradually settles again once the trigger has passed.

Alopecia areata is an autoimmune condition in which the immune system attacks hair follicles and creates well-defined, round or oval patches without hair. The skin in these areas typically looks normal, without scarring. It can appear as a few small patches or more extensive hair loss across the scalp or body. Both inherited factors and environmental influences appear to play a role in the risk of developing it.

The same underlying mechanisms can affect both sexes, though they don't always present the same way.

In men, hereditary pattern hair loss often starts earlier in life, showing up as a receding hairline at the temples and increasing thinning at the crown — a pattern many people recognise in close male relatives.

In women, the picture differs. Hereditary hair loss most often causes a wider parting and general thinning across the top of the head, without fully bald areas. Hormonal changes tied to pregnancy, the postpartum period, and menopause play a larger role, and can both trigger and worsen thinning.

Two people with the same underlying cause can therefore experience their hair loss very differently, both visually and emotionally.

Hair loss often stems from an interplay between inherited factors and outside influences. Genetics, the immune system, and hormones set the framework, while daily life and routines shape how it develops.

Ongoing stress, severe calorie-restrictive diets, and major illness can push more hairs into the resting phase. Tight hairstyles, frequent heat styling, and strong chemical treatments can weaken hair fibres and make them look more fragile.

Hair loss is therefore often multifactorial — genetic predisposition lays the foundation, and life circumstances affect when and how quickly the change becomes noticeable. A medical assessment that considers the whole picture is especially useful here.

A doctor or dermatologist is the only one who can make a reliable diagnosis, but it can be hard to judge for yourself when hair loss needs prompt attention versus when it's fine to keep an eye on it a little longer. Contact a doctor promptly if you notice:

Speak to your doctor, even if it doesn't feel urgent, if you notice:

Uncertainty on its own is a good enough reason to book an appointment — it's better to get checked once too often than to wait too long.

In some cases, hair loss is a sign that something else is going on in the body — especially when the shedding doesn't happen on its own but comes with other symptoms. Marked tiredness, unexplained fever, or unexplained weight changes alongside hair loss can point to thyroid problems or other conditions that need further assessment. The aim isn't to cause unnecessary worry, but to take the body's signals seriously — if you're noticing this combination, booking a GP appointment is a sensible next step.

This checklist doesn't give you a diagnosis — it helps you sort through what you're noticing and prepare for a conversation with your GP.

Often harmless and temporary:

May resemble hereditary pattern hair loss:

Should be assessed by a doctor:

If you have persistent doubts or concerns, it's worth contacting a doctor for a clear assessment.

You don't need to wait until you're in the room to start helping your case. A little preparation makes it easier for your doctor to assess your situation — and easier for you to get answers to what worries you most.

Before your appointment:

If you're experiencing any of the urgent warning signs above, make the appointment without waiting. There are also various medical and cosmetic options to support hair, which your doctor can advise on depending on the underlying cause.