What it actually is:

- Keratin often releases formaldehyde

- Smoothening uses strong chemicals to reshape bonds

 

What it does:

- Very strong straightening

- Maximum frizz removal

 

Best for:

- Very curly, coarse hair

 

Longevity:

- Keratin: 3–5 months

- Smoothening: 6–12 months (but regrowth looks stiff)