The US drugs watchdog has warned about the harmful effects of hormone gel on children.
Adults using prescription testosterone gel have been told to be extra careful and to avoid the substance coming into contact with children - or risk serious side effects.
Some of the possible problems described by the Food and Drug Administration (FDA) included enlargement of the genital organs, aggressive behaviour, early ageing of the bones, premature growth of pubic hair, and increased sexual drive.
It said both boys and girls were at risk, and ordered its strongest warning on the products..
Men are often prescribed the gel if their bodies stop producing testosterone, or if they have very low levels of the hormone.
The FDA said children are likely to come into contact with the substance when adults fail to properly wash their hands after using the gel.
In most cases the symptoms observed in children who have come into contact with the treatment go away once testosterone gel is identified as the cause of the problem and remedies are taken.
But health officials said that in some children, enlarged sex organs did not return to their appropriate size, and bone age remained somewhat higher than the child’s chronological age.