Why Does Hair Loss Only Affect the Top of the Scalp, Not the Back and Sides?
- Gwen Adey
- 1 day ago
- 4 min read
How Does Hair Know Where It Is?
This might sound like a strange question.
But it is one of the most fascinating questions in hair loss research.
Think about male pattern hair loss.
Why does hair usually disappear from the top of the scalp while the hair at the back and sides often stays thick?
After all, every hair follicle is attached to the same person.
They share the same blood supply.
They are exposed to the same hormones.
They live on the same head.
So why do some follicles shrink while others carry on growing normally?
The honest answer is that we do not fully know.
But scientists are starting to uncover some clues.
Hair Follicles Are Not All The Same
For many years, doctors assumed that all hair follicles were basically the same.
We now know that is not true.
A hair follicle from the front of the scalp behaves differently from a hair follicle taken from the back.
This is one of the reasons hair transplants work.
When a surgeon moves a healthy follicle from the back of the scalp to the front, it usually keeps its resistance to hair loss.
In other words, it takes its special characteristics with it.
That suggests the follicle itself contains some kind of built-in information.
A Recent Study Gave Us Another Clue
In 2026, researchers took hair follicles from both the front and the back of the scalp of men with androgenetic alopecia (male pattern hair loss).
They then grew these follicles in a laboratory.
When they exposed the follicles to DHT, the hormone most closely linked to pattern hair loss, something interesting happened.
The follicles from the front of the scalp slowed their growth and showed many of the changes seen in male pattern baldness.
The follicles from the back of the scalp did not react in the same way.
Even though they were no longer attached to the body, they still behaved differently.
The front follicles acted like front follicles.
The back follicles acted like back follicles.
It was almost as if they remembered where they came from.
The Tooth Analogy
I remember learning about this sort of thing more than twenty years ago, when I was a dental student.
We studied something called HOX genes.
These genes help tell parts of a developing baby what they are supposed to become.
They help answer a simple question:
“Where am I?”
This might sound odd, but every tooth in your mouth starts with the same DNA.
Yet somehow a front tooth becomes an incisor and a back tooth becomes a molar.
They look different and do different jobs.
The difference is not the DNA itself.
The difference is which instructions are switched on during development.
Hair follicles may work in a similar way.
Could The Answer Begin Before Birth?
Possibly.
Scientists think different parts of the scalp may receive different instructions while a baby is developing in the womb.
Those instructions may stay with the follicle throughout life. If that is true, a follicle from the back of the scalp may not simply be a front follicle in a different location. It may be biologically different from the very beginning.
That could explain why some follicles are much more sensitive to hair loss than others.
Why Does This Matter?
Because understanding this process could help us develop better treatments.
Imagine if scientists could discover exactly what makes donor hair resistant to hair loss.
Could we one day teach vulnerable follicles to behave in the same way?
Could we switch on protective signals?
Could we switch off harmful ones?
Nobody knows yet.
But these are exactly the kinds of questions researchers are trying to answer.
What We Know So Far
We still do not know exactly how a hair follicle knows where it is.
But we do know that it seems to.
Hair follicles from different parts of the scalp behave differently.
They respond differently to hormones.
They express different genes.
They age differently.
And even when they are removed from the scalp and studied in a laboratory, they often keep those differences.
For me, this is one of the most fascinating mysteries in hair biology.
A hair follicle may look simple.
But it appears to carry a memory of its origins that scientists are only just beginning to understand.
Authored by Dr Gwen Adey
First published 14/06/26
Reference
Medical Disclaimer
This article is intended for educational purposes only and should not be taken as individual medical advice. If you are experiencing hair loss, speak to a suitably qualified healthcare professional.
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