Sodium Lauryl Sulfate
Properties
| State | Solid at room temperature (waxy flakes or fine powder) |
| Color | White to cream |
| Solubility | Soluble in water (about 100 g/L at 20 °C); solutions foam vigorously |
| Melting Point | 204-207 °C (decomposes) |
About Sodium Lauryl Sulfate
Sodium lauryl sulfate (NaC12H25SO4, MW 288.372), known as SLS in personal care and SDS in the biochemistry lab, is the workhorse anionic surfactant of the modern world: a 12-carbon alkyl tail tethered to a negatively charged sulfate head group, with a critical micelle concentration (CMC) of roughly 8.2 mM in water at 25 °C and an aggregation number near 62. Above the CMC the molecules self-assemble into spherical micelles that solubilize oils and lipids in their hydrophobic interiors, which is the mechanism behind every foaming shampoo, toothpaste, body wash, and degreaser on the market. SLS is manufactured by sulfating dodecanol (lauryl alcohol, derived from coconut or palm-kernel oil) with chlorosulfonic acid or SO3, then neutralizing with NaOH. In biochemistry, SDS is the denaturant in SDS-PAGE invented by Ulrich Laemmli in 1970: SDS binds proteins at a roughly constant ratio of 1.4 g SDS per g protein, swamping their intrinsic charge with uniform negative charge density and unfolding them into rod-like complexes. Loaded onto a polyacrylamide gel under an electric field, proteins then migrate strictly by molecular weight (Stokes radius scales with mass for SDS-coated rods), giving the band ladder every molecular biologist recognizes. SDS also lyses bacterial cells in the alkaline lysis miniprep, denatures membrane proteins for Western blot extraction, and serves as the surfactant in countless industrial cleaners and fire-fighting foams. Annual global production is in the hundreds of thousands of tonnes.
Where you'll encounter it
If you've ever brushed your teeth and watched the foam in the sink, run a Western blot from cell lysate, or extracted DNA from strawberries with dish soap and isopropanol in a high school demo, you've used SDS/SLS. In a molecular biology lab, the Laemmli sample buffer recipe (50 mM Tris pH 6.8, 2% SDS, 10% glycerol, 0.1% bromophenol blue, 5% beta-mercaptoethanol) is one of the first things a graduate student memorizes; you boil the lysate at 95 °C for 5 minutes to fully denature, then load 20 microliters per well in a 4-12% gradient gel. In a personal care formulation, SLS at 8-15% in shampoo gives the foam consumers expect, but it's also the most-blamed irritant in canker-sore-prone individuals, which is why 'SLS-free' toothpastes (Sensodyne ProNamel, Tom's of Maine) substitute milder amino-acid surfactants like sodium cocoyl glutamate. In the cosmetic industry, the Cosmetic Ingredient Review panel concluded in 2010 that SLS is safe at concentrations up to 1% for leave-on products and higher for rinse-off; long-standing internet claims that SLS is carcinogenic have no toxicological backing.
Common Uses
- Primary anionic surfactant in shampoos, body washes, and toothpastes (8-15%)
- Denaturant in Laemmli SDS-PAGE for protein separation by molecular weight
- Lysis surfactant in alkaline plasmid minipreps (Birnboim-Doly protocol)
- Foaming agent in AFFF (aqueous film-forming foam) firefighting concentrates
- Emulsifier in topical pharmaceutical creams, lotions, and ointments
- Cleaning surfactant in industrial degreasers, dishwashing detergents, and floor cleaners
- Wetting agent in herbicide and pesticide tank mixes for leaf coverage
- Critical-micelle-concentration teaching standard in physical chemistry labs
Safety Information
Skin and eye irritant; the severity scales with concentration and contact time. Rabbit eye Draize scores reach severe at 10%; the CIR panel sets safe leave-on limits at 1%. Inhalation of dry SLS dust causes respiratory irritation. Not classified as carcinogenic by IARC, NTP, or OSHA, despite persistent online claims to the contrary. OSHA does not set a specific PEL; manufacturer SDS sheets typically recommend 5 mg/m3 (8-hour TWA) for nuisance dust. Oral LD50 in rats is around 1,288 mg/kg. GHS classifications: H302 (harmful if swallowed), H315 (causes skin irritation), H318 (causes serious eye damage), H335 (may cause respiratory irritation), H412 (harmful to aquatic life with long-lasting effects). Pictograms: Corrosion, Exclamation mark, Environment. Standard PPE: safety glasses, nitrile gloves, dust mask when handling dry powder. Avoid mixing concentrated solutions with cationic surfactants (they precipitate as inactive complexes).
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.