Ptychotropism as a cutaneous feature of the CHILD syndrome. The hallmark of the CHILD syndrome is a unilateral ichthyosiform nevus that displays a pronounced affinity for the body folds. For this phenomenon the term ptychotropism is proposed. The expression is composed from the Greek words ptyche (fold) and trope (a turning). It is concluded that the cutaneous lesions of the CHILD nevus are determined by two factors, lyonization and ptychotropism. The phenomenon of ptychotropism constitutes an additional argument to distinguish the CHILD nevus from the inflammatory linear verrucous epidermal nevus because the latter is not ptychotropic. 