Through further processing, primarily in the gonads and adrenal glands, cholesterol is converted into sex hormones like estrogen and testosterone. Kenneth Lee Jones, the former chief of pediatrics at the University of California, San Diego, noted pediatric cases similar to those described by Dr. Dedekian in a 2004 report in the journal Pediatrics.

At that time, unregulated “prohormones” like Andro, famously used by Mark McGwire, the former St. Louis Cardinals power hitter, and banned by federal law in 2005, were available as topical sprays used to enhance libido. Dr. Jones said the sprays used by adults in some households permeated the children’s bedsheets, and the early puberty stopped only when the adults stopped using the sprays and also discarded old sheets.

Testosterone-containing products are not the only trigger of disordered puberty in children.

In a 1998 paper in the journal Clinical Pediatrics, Dr. Chandra Tiwary, the former chief of pediatric endocrinology at Brook Army Medical Center in Texas, reported an outbreak of early breast development in four young African-American girls who used shampoos that contained estrogen and placental extract. The early puberty reversed once the shampoo was stopped.

In the tradition of previous physicians who deliberately exposed themselves to possible pathogens, Dr. Tiwary tried the shampoos on himself. He carefully measured his own levels of various male and female sex hormones to establish his baseline, used the shampoos for a few days, then repeated the tests.

While Dr. Tiwary is quick to admit that his unpublished findings must be interpreted with great caution, some of his sex hormone levels changed by almost 40 percent after he used the shampoos. In some cases, substances other than sex steroids may also disrupt normal sexual development. In Boston at the annual Endocrine Society meeting in June, Clifford Bloch of the University of Colorado School of Medicine presented several cases of young men who had developed marked breast enlargement from using shampoos containing lavender and tea tree oils, which are widely used essential oil additives that present no problem for adults. (Unlike Dr. Dedekian’s cases, these cases were not a result of passive transfer from parents. The boys themselves used the shampoos.)

Dr. Bloch collaborated with scientists at the National Institute of Environmental Health Sciences in North Carolina to test the oils on human breast cells grown in test tubes. Lavender and tea tree oil had the same effect on the cells as estrogen.

Dr. Bloch speculates that the findings, which he is submitting for publication in a peer-reviewed journal, may explain the boys’ breast growth. He noted, however, that cells in a test tube are a far cry from humans, so the relationship of the essential oil to breast growth remains hypothetical.