Autism and Exposure to Environmental Chemicals 171[22–28]. Of these, oxybenzone, benzophenone‐1, galaxolide, and tonalide also
affect androgens, while butylated hydroxytoluene, benzophenone‐2, and octi
noxate have been linked to thyroid hormone disruption [28–34]. Even at very
low concentrations, fragrances that contain these chemicals can be mutagenic
and carcinogenic [3,4,7,21]. Of note, one of the fragrance ingredients, acetyl
ethyl tetramethyl tetraline, was used for 22 years in fragrances, colognes, soaps,
detergents and cosmetics [33]. It resulted in behavioral changes and degenera
tion of the white matter of the brain including “widespread demyelination and
scattered axonal degeneration in the central peripheral nervous systems.” It was
voluntarily discontinued in 1978. Along with this, the fragrance ingredient
musk ambrette (a fixative recently banned in the European Union but still
allowed in the USA) has been found to also cause degeneration of the myelin
sheath and distal axon [33]. Even if one considers the high fetal testosterone
levels during the early stages of gestation, these data do not explain the rising
incidence of ASD, except that synthetic chemicals behaving like hormones can
reach the fetal blood circulation [7,25,27,34,35]. We know that many fra
grances, and especially perfumes, contain testosterone‐like hormones [21]
(Table 7.1). Chlordane was a termite preventative chemical used in US homes
in the 1960s–1980s. It was banned for use inside homes in 1979 and under
neath homes as a soil treatment in 1983 [36–39]. Due to concerns about dam
age to the environment and harm to human health, all use of chlordane was
banned by the Environmental Protection Agency (EPA) in 1988 [37].
A question that remains is why are female neuronal cells relatively more
protected than their male counterparts? It has been proposed by some investi
gators that the male bias for ASD may be partially due to under diagnosis of
autism in females or the human female’s ability to mask some of the symptoms
of ASD [5]. Even so, these investigators agree that male bias is observed in
ASD. While in the majority of cases, the exact etiology of ASD remains
unknown, novel technologies and large population based studies have pro
vided new insight into the risk architecture of ASD and the possible role of
environmental factors in etiology. Recently, we have shown that one of the fac
tors explaining why ASD is more common in boys than girls may be due to the
preferential depletion of oxytocin‐ and arginine vasopressin (AVP)‐receptor
positive neurons in developing fetal brains [40]. Utilizing neuroblastoma cell
lines (NBCs) derived from both genders that were exposed to femtomolar con
centrations of commonly used fragrances, we determined that both types of
the neurons are more significantly depleted from the male neuroblastoma cells
compared with female [2,5,40]. We already have discussed the potential role of
fetal testosterone in ASD in Chapter 5. Here we present some of the alarming
evidence regarding the fragrances we smell every day, the majority of which are
synthetic chemicals that enter our brains via the olfactory system. However,
the most important with respect to ASD are the ones that enter our blood
stream via the lungs and are absorbed into our skin and then enter our blood via