These inorganic
polyphosphate salts all function as
chelating agents in cosmetic formulations. In addition,
Sodium Metaphosphate functions as an oral care agent,
Sodium Trimetaphosphate as a buffering agent, and
Sodium Hexametaphosphate as a corrosion inhibitor. Only
Sodium Hexametaphosphate is currently reported to be used. Although the typical concentrations historically have been less than 1%, higher concentrations have been used in products such as bath
oils, which are diluted during normal use.
Sodium Metaphosphate is the general term for any
polyphosphate salt with four or more
phosphate units. The four-
phosphate unit version is cyclic, others are straight chains. The
hexametaphosphate is the specific six-chain length form. The trimetaphosphate structure is cyclic. Rats fed 10%
Sodium Trimetaphosphate for a month exhibited transient tubular
necrosis; rats given 10%
Sodium Metaphosphate had retarded growth and those fed 10%
Sodium Hexametaphosphate had pale and swollen kidneys. In chronic studies using animals, growth inhibition, increased kidney weights (with
calcium deposition and desquamation), bone decalcification, parathyroid
hypertrophy and
hyperplasia, inorganic
phosphaturia, hepatic focal
necrosis, and muscle fiber size alterations.
Sodium Hexametaphosphate was a severe skin
irritant in rabbits, whereas a 0.2%
solution was only mildly irritating. A similar pattern was seen with
ocular toxicity. These ingredients were not genotoxic in bacterial systems nor were they carcinogenic in rats. No reproductive or developmental toxicity was seen in studies using rats exposed to
Sodium Hexametaphosphate or
Sodium Trimetaphosphate. In clinical testing, irritation is seen as a function of concentration; concentrations as high as 1% produced no irritation in contact
allergy patients. Because of the
corrosive nature of
Sodium Hexametaphosphate, it was concluded that these ingredients could be used safely if each formulation was prepared to avoid skin irritation; for example, low concentration in a leave-on product or dilution of a higher concentration as part of product usage.