JOURNAL OF THE AMERICAN COLLEGE OF TOXICOLOGY
Volume 2. Number 7, 1983
Final Report on the Safety
Assessment of Sodium Lauryl Sulfate
Sodium Lauryl Sulfate is an anionic surfactant used in cosmetics and industrial
chemicals as a cleansing agent. In absorption, metabolism and excretion studies
Sodium Lauryl Sulfate had a degenerative effect on the cell membranes because of
its protein denaturing properties. High levels of skin penetration may occur at
even low use concentration.
Sodium Lauryl Sulfate had an LD 50 (Lethal Dose for 50% of the animals tested)
of 0.8 to 110 g/kg in rats. A formulation containing 15% caused depression,
labored breathing, diarrhea and death in 4 out of 20 animals.
In acute ocular tests, 10% Sodium Lauryl Sulfate caused corneal damage to the
rabbits’ eyes if not irrigated or irrigation was delayed. A Draize test of a
product containing 5.1% Sodium Lauryl Sulfate caused mild irritation and
products containing 21% were severely irritated with no rinse and mildly
irritated when rinsed.
Acute animal skin irritation studies of 0.5% to 10% Sodium Lauryl Sulfate cause
slight to moderate irritation. Applications of 10% to 30% caused skin corrosion
and severe irritation. Solutions above 20% were highly irritating and dangerous.
One percent and 5% Sodium Lauryl Sulfate produced a significant number of
comedones when applied to the pinna of albino rabbits.
A chronic oral feeding study in rats of 0.25%, 0.5% and 1.0% Sodium Lauryl
Sulfate in the diet for two years produced no observable abnormalities except
for moderate to severe dermal effects. In mutagenesis studies, rats fed 1.13%
and 0.56% Sodium Lauryl Sulfate in the diet for 90 days produced no more
chromosomal aberrations or clastogenic effects than did a normal diet.
Sodium Lauryl Sulfate was tested for human skin irritation in concentrations
ranging from 0.1% to 10%. Open patches were less irritating than closed patches,
and irritation increased directly with concentration. For prolonged contact with
skin, concentration should not exceed 1%.
CHEMICAL AND PHYSICAL PROPERTIES
Sodium Lauryl Sulfate, an anionic surfactant, is prepared by the sulfation of
commercially available lauryl alcohol form coconut our, with either sulfur
trioxide or chlorosulfonic acid. The product of the reaction is then neutralized
with aqueous sodium hydroxide (lye). The abbreviated symbol for Sodium Lauryl
Sulfate is used around the world in clinical studies as a skin irritant. SLS is
the universal standard, by which a measured percentage is evaluated to promote a
given level of irritation and reaction. By this SLS standard level or
irritation, it is then possible to evaluate the healing or modifying
characteristics of any ingredient or formula used on the SLS irritated skin.
Carcinogenic nitrates can form in the manufacturing of Sodium Lauryl Sulfate or
by its inter reaction with other nitrogen bearing ingredients within a
formulation utilizing this ingredient
Tests show permanent eye damage in young animals from skin contact in non eye
areas. Studies at Georgia Medical College indicated Sodium Lauryl Sulfate kept
young eyes from developing properly by possibly denaturing the proteins and not
allowing for proper structural formation. This damage was permanent.
Other studies have indicated that Sodium Lauryl Sulfate enters and maintains
residual levels in the heart, the liver, the lungs and the brain from skin
contact. This poses question of it being a serious potential health threat to
its use in shampoos, cleansers, and tooth pastes.
Still other research has indicated SLS may be damaging to the immune system,
especially within the skin. Skin layers may separate and inflame due to its
protein denaturing properties.
A higher foaming and slightly less irritating modification of Sodium Lauryl
Sulfate can he manufactured by ethoxylation of the surfactant. The modified
compound becomes know as Sodium Lauryl Ether Sulfate. The cosmetic name is
Sodium Laureth Sulfate with an abbreviated symbol of SLES.
For products without sls
or controversial ingredients