How to tell if your hair is damaged

Everyone says they have damaged hair. But very few people know exactly what that means, what causes it, and above all, how to distinguish real damage from hair that simply needs hydration.

What "damaged hair" actually means

Hair is made up of three layers: the medulla (internal core), the cortex (where pigment and keratin live), and the cuticle (the outer layer, made of microscopic scales that overlap like shingles on a roof).

When we talk about damaged hair, we are almost always talking about damage to the cuticle. When those scales are closed and aligned, the hair is shiny, soft to the touch, elastic, and easy to comb. When they are open, lifted, or broken, the hair loses moisture, loses shine, loses elasticity, and begins to behave in ways we recognize as "damage."

The real signs of hair damage

1. The glass of water test

Take a clean, dry strand of hair and submerge it in a glass of water. Observe:

• If it floats for more than a minute: the cuticle is relatively closed, a good sign
• If it sinks quickly: the hair is very porous and absorbs water easily, a sign of damage or high porosity

2. The elasticity test

Take a damp hair and gently stretch it between two fingers. Healthy hair can stretch up to 30% of its length and return to its shape. If:

• It breaks without stretching: it is dry and lacks protein
• It stretches too much and doesn't snap back: it lacks hydration or the internal structure is compromised

3. How it feels when dry

Run your fingers through your dry hair from roots to ends. Healthy hair feels smooth and slides well. If you notice:

• Roughness or texture: the cuticle scales are lifted
• Straw-like texture: significant damage to the cuticle
• Constant tangles for no reason: the hair snags on itself because the cuticle is not smooth

4. The shine (or lack thereof)

Hair shine comes from the reflection of light off a closed and uniform cuticle. Damaged hair is matte by definition—light does not bounce off, it scatters. If your hair has progressively lost shine without any changes to your routine, the cuticle is compromised.

5. Breakage and split ends

Split ends are the most visible symptom. But there is a more important one: breakage in areas other than the tips. If you find broken hairs along the strand—not at the root, but in the middle, your hair is giving way due to a lack of structural integrity.

6. Drying time

Damaged and porous hair absorbs much more water than usual, which means it takes longer to dry. If your damp hair stays wet long after it usually would, porosity is high.

The most common causes (and the least obvious ones)

The obvious ones:

• Repeated bleaching and chemical dyes
• Excessive heat without thermal protection
• Aggressive brushing, especially when wet
• Hair ties with metal or hairstyles that are too tight

The less obvious ones:

• The sun: UV radiation degrades keratin and melanin cumulatively and silently
• Hard water: calcium and magnesium in tap water deposit on the fiber and lift the cuticle
• The wrong shampoo: harsh sulfates strip the natural protective sebum and leave the cuticle exposed
• Towel drying: rubbing your hair with a towel lifts the cuticle scales with every movement
• Lack of protein: hair is made of keratin; without protein intake, the structure weakens over time

The difference between damage and dryness

They are different things, even though they are constantly confused.

Dryness is a lack of moisture. The hair is dehydrated but its structure may be intact. It improves with hydration: masks, leave-ins, oils.

Damage is a structural deterioration of the cuticle or cortex. Moisture does not fix it; it may temporarily improve the appearance, but structural damage is not reversed by hydration alone. It requires protein reconstruction and, in the most severe cases, a haircut.

How to distinguish them: dry hair improves visibly after a hydrating mask. Damaged hair improves less than expected and the improvement does not last.