HHCB (1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta-gamma-2-benzopyran and related isomers) is a member of a group of substances used in fragrances and known collectively as the polycyclic musks. Because it is a highly viscous liquid, it is sold fluidised as an approximately 65% solution.
HHCB is used to make a fragrance long lasting and have a positive technical effect on its balance bringing the initial and residual smell into harmony.
HHCB is produced in one plant in the UK in an annual volume of 1000 to 5000 tonnes and is transported to Ireland for dilution to the commercial product.
It is used as an ingredient in commercial preparations intended to be used as fragrances in a wide variety of consumer products such as perfumes, cosmetics, household and laundry cleaning products and air fresheners. These commercial preparations are not sold retail. The level of HHCB in such preparations is typically at a level of several percent. The principal exposure to HHCB from household products can be considered to be via the skin.
The relative volume of use in household products versus perfumes, cosmetics, etc. is not known although the majority can be assumed to be used in household products based on the relative volume of sales of such products.
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HHCB has a low acute toxicity either by the oral or dermal route (LD50 values >3000 mg/kg). Inhalation exposure has been estimated to be negligible relative to dermal.
HHCB is not a skin or eye irritant and shows no phototoxicity potential on humans at concentrations significantly higher than would be encountered from the use of fragranced consumer products. There is no significant evidence either from animal or human studies of potential for dermal sensitisation. HHCB shows no photosensitisation potential on humans at concentrations significantly higher than would be encountered from the use of fragranced consumer products.
In a 90-day study in rats, there were no adverse effects at the highest dose tested, 150 mg/kg bw/day.
There were no indications of effects on fertility or the developing foetus at levels as high as 50 mg/kg bw/day.
There were no effects on rat pups exposed via the milk during nursing to levels of HHCB over 100 times the maximum level found in human milk samples.
HHCB is a non-genotoxic substance. The mutagenicity data and the repeated dose studies with HHCB do not indicate a concern with regard to carcinogenicity nor does HHCB possess any structural features that would raise a concern.
In the unlikely event of maximum exposures from direct and indirect skin contact as well as from the oral route via dishware residues, the estimated exposure to HHCB from its use in household cleaning products of 0.07 µg/kg bw/day. Comparison of this exposure to the NOAEL indicates a margin of safety of at least 350,000 and supports the conclusion that there is no significant risk to human health from exposure to HHCB as used in household cleaning products.