Keratin Hair Smoothing Treatments

Salon smoothing systems that release formaldehyde when heated.

52Moderate burden · out of 100

Cleaner swapFormaldehyde-free smoothing systems, or skip the treatment

How this score is built

100Start
67.8Chemical hazard 7 × 4.6−32.2
57.6Everyday exposure 3 × 3.4−10.2
52Persistence 2 × 2.6−5.2, then rounded to 52
ModerateThe band52 sits in 40–59.

What each input rests on

The three ratings behind the score, and the studies each rests on
Input	Rating	Evidence
Chemical hazard	7/10	unsourced input
Everyday exposure	3/10	Simulating four keratin smoothing brands on mannequin heads, mean airborne formaldehyde reached 0.08-3.47 ppm during blow-drying and 0.08-1.05 ppm during flat-ironing; one product contained 11.5% formaldehyde in bulk. Characterization of formaldehyde exposure resulting from the use of four professional hair straightening products · J Occup Environ Hyg 2011 DOI 10.1080/15459624.2011.626259 · PMID 22035353 · Abstract · read 2026-10-16
Persistence	2/10	unsourced input

Ratings are editorial. A study listed here supports the rating; it did not compute it. How the index is built

What this means for you

The chemical-hazard rating is what drives the score down. Occupational safety regulators issued hazard alerts after air testing found formaldehyde released during these treatments, including from products labelled formaldehyde-free. Salon workers carry the heaviest exposure because it is repeated daily.

Evidence strength: strong

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Lower-exposure choices

Fragrance-Free Basic SkincareMinimal · Personal Care

All 33 personal care entries, highest burden first →