# Sodium Lauryl Sulfate (SLS)

Canonical URL: https://guide.rozhair.com/glossary/sls/

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SLS is the original surfactant that made shampoo foam the way most people expect. It's also why a lot of people have reacted badly to shampoo without knowing why — SLS is in the top ten most common contact allergens tracked by dermatological patch testing.

On the hair, SLS is indiscriminate: it strips dirt, product, pollution, *and* the protective lipid layer that keeps your cuticle closed and your color locked in. That's the trade for the lather. If your scalp flakes, itches, or burns after washing, there's a reasonable chance SLS is the cause.

SLS is still common in drugstore shampoos and cheaper body washes. Most premium brands have moved to [SLES](/glossary/sles/) — milder but still a sulfate — or to [sulfate-free surfactants](/glossary/surfactant/) entirely.