Invisible to the naked eye, it nevertheless shapes the future of your hair. You look to hormones, your products or a drop in blood pressure. You readjust your routine. But nothing works. Sometimes what's happening is neither visible nor immediate.

It's a mechanism that most medical experts know about, but you probably don't: oxidative stress. This often overlooked imbalance could well be the key to understanding what your follicles are going through. And why do they end up abandoning you?

Oxidative stress: why should you care?

Oxidative stress occurs when your body generates more free radicals - unstable molecules that damage cells - than it can neutralize with and antioxidants.. These free radicals can attack proteins, DNA and lipids, including those inside your hair follicles. When this happens to the scalp, it leads to inflammation, cellular dysfunction and, over time, the weakening or even death of the cells responsible for hair production.

And here's where it gets personal. You don't have to lead an extreme lifestyle to be concerned. If you live in a heavily polluted city, spend hours in the sun without scalp protection, eat a diet rich in sugars or ultra-processed foods, or suffer chronic stress - congratulations - you're already overwhelmed by oxidative stress without even realizing it.

How oxidative stress damages your hair

Hair follicles aren't just living structures: they're emotional sponges. Ultra-sensitive to what's going on around them, they react to the slightest disturbance.

At the base of each follicle is the dermal papilla, a small, fragile and essential nucleus of cells. It's here that hair growth takes root. These cells work non-stop, consuming energy, regulating keratin production and responding to hormonal, nutritional and nervous signals. This is where it all happens.

But when an excess of oxidative stress - too many free radicals - sets in, this HQ becomes saturated. It loses its way. And as everything is interconnected, a simple imbalance is enough to cause your entire system to falter.

This is exactly what happens when, a few weeks after an abrupt break-up, a loss, a viral infection or even a crash diet, you start losing your hair by the handful without understanding why. You haven't changed your hair routine, but your scalp has suffered an emotional shock.

What science says

Androgenetic alopecia

In the case of androgenetic alopecia researchers observed a disturbing fact: very high lipid peroxidation in the scalp.

Put another way? Lipids - the natural fats that protect your cells - oxidize, a bit like fruit turning brown in the open air. This is what we call oxidative damage, and here it's clearly visible at the very heart of your scalp tissue.

And that changes everything. Because in addition to worsening the effect of DHT - the hormone that thins your hair - this oxidative stress also seems to age follicles faster.

Telogen effluvium

In telogen effluviumOften triggered by intense emotional stress, illness or iron deficiency, oxidative stress acts as a warning signal.

Faced with this imbalance, your scalp reacts by abruptly shortening the life cycle of your hair, pushing it into the early stages of hair loss. The result: handfuls of hair falling out, sometimes without warning.

This is no coincidence. A study published in Oxidative Medicine and Cellular Longevity has shown that people with TE had significantly higher levels of oxidative stress than people with no hair loss.

In other words, you didn't "think too much about your hair". There was a real inner disturbance.

Alopecia areata

Even in the most complex forms, such as alopecia areata an autoimmune disease in which the body attacks its own follicles - scientists find traces of intense oxidative stress.

An excess of free radicals promotes inflammation of your hair follicles, making them more vulnerable. This imbalance could potentially be the trigger for the disease.

The sources of oxidative stress we forget about every day

We often think that oxidative stress only affects smokers or alcohol addicts. In reality, it's everywhere. And it's the small, chronic exposures that we trivialize that end up deeply damaging the scalp.

The city kills your roots

Take city lifefor example. Being stuck in traffic jams, breathing air saturated with fine particles, walking every day under a gray sky laden with nitrogen dioxide... it's a constant assault on your scalp. Studies carried out on urban populations in China and India have clearly established the link between air pollution, thinning hair and premature graying. And it's not just Asia. Paris, Marseille, Dakar, New York, it's all the same: the pollutant cocktail spares no one.

Your hair shines, but your follicles scream

Add to this the heating appliances and chemical treatments Hairstyling: straightening plates, repeated blow-drying, ammonia-based coloring or salon bleaching... all these generate free radicals. Not just on the visible hair, but right into the follicular environment. The result: you may have shiny hair on Instagram, but your roots are already deeply oxidized. And that root doesn't lie.

Leading sun, loose keratin

Another major aggressor is the sun. UV rays don't stop at the skin. They also attack the internal structure of the scalp, degrading keratin, oxidizing melanin, and triggering inflammatory processes. Many people who spend their summers at the beach, bareheaded, end up noticing duller, brittle hair, and sometimes more diffuse loss at the end of the season. This is rarely a coincidence.

Mental stress, the biological version

And then there's emotional stressthe real thing. The one that lasts. The kind that makes you brood at night, that ruins your appetite or makes you eat everything without thinking. This kind of stress raises cortisol, and cortisol lowers your antioxidant defenses. The scalp, already vulnerable, becomes an easy target. You don't feel it right away. But as the weeks go by, the hair starts to fall out.

Our final take away

As long as oxidative stress is present, your hair will remain under tension. Not to the point of sudden hair loss. But enough to weaken and destabilize your hair growth cycle, until hair loss sets in.

If you don't take a close look at your environment and lifestyle, but above all your metabolism, you're missing out on what's really weakening your hair deep down.

You've begun to understand. Please continue. The next article explores another forgotten angle: the link between diabetes and hair loss.