Human hair is mostly keratin, but its strength and beauty can be compromised by heat, sun, hard water, and harsh products. A keratin treatment restores structure and shine. Choosing a formaldehyde-free version and pairing it with sodium-chloride- and sulfate-free maintenance products (like those from Peter Coppola) helps you preserve the treatment safely and effectively.

Human hair is a remarkable biological structure — essentially, a dead but highly engineered fiber. At its core, your hair is built from keratin, a fibrous structural protein that gives hair its strength, elasticity, and resilience.

Chemical Composition

Proteins
Hair is made up of 65 %–95 % protein, most of which is keratin. 

Water
Approximately 12 %–15 % of the hair shaft is water. 

Lipids
A smaller portion consists of lipids (fats), like free fatty acids and cholesterol. 

Pigments & Trace Minerals
Hair also contains melanin (which gives it color), nucleic acids, and trace elements such as zinc, iron, and copper. 

Structure of the Hair Strand

A single hair strand has three main layers:

1. 1. Cuticle – the outermost “scale” layer made of overlapping dead cells composed of keratin. 
      
      
   2. Cortex – the bulk of the strand, containing densely packed keratin filaments and pigment granules; it’s what gives hair its strength, elasticity, and color. 
      
      
   3. Medulla – the innermost core, which is loosely packed and may even be absent in finer hairs. 

At the molecular level, keratin in hair forms intermediate filaments and is heavily cross-linked by disulfide bonds, hydrogen bonds, and salt linkages. These cross-links (especially disulfide bridges involving cysteine) are critical to hair’s mechanical strength. 

How Hair Gets Damaged

Even though hair is dead material, it’s far from indestructible. Several external stressors can degrade the keratin matrix, lift the protective cuticle, and break down the internal structure — leading to damage, brittleness, and dullness.

Thermal Styling

Frequent use of hot tools — like straighteners, curling irons, and blow dryers — can weaken hair by disrupting hydrogen bonds and dehydrating the strand. Over time, the repeated heat exposure causes the cuticle to crack, making hair more brittle, rough, and prone to breakage.

Environmental Factors

Hard Water
Hard water contains high levels of minerals (calcium, magnesium) that can leave deposits on hair. These mineral deposits can make hair feel stiff, look dull, and interfere with treatments, reducing the effectiveness of conditioning and smoothing products.

Sun Exposure
UV rays can degrade the protein structure in hair, break down disulfide bonds, and fade pigment, leaving the strand fragile and dry.

Swimming Pools / Chlorinated Water
Chlorine and other pool chemicals strip away natural oils, lift cuticle scales, and oxidize keratin, which accelerates dryness and damage.

Harsh Hair Products

Frequent use of aggressive shampoos, sulfates, or other caustic chemicals can erode the cuticle and strip essential lipids and proteins. Over time, this weakens the inner keratin structure, making hair more porous, fragile, and less manageable.

If you’re ready to experience the benefits, consider browsing Peter Coppola’s treatment line and supporting products to build a more resilient, radiant, and healthy hair routine.

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