The term "paraphilic infantilism" refers to a sexual fetish where certain individuals find the idea of being a baby arousing. It is probably because of how alien "paraphilic infantilism" sounds that people have taken to calling it adult baby syndrome.
Adult baby syndrome is slightly different from autonepiophilia, a condition where people find arousal in wearing nappies. Though, the confusion is easy to understand because adult babies also wear nappies. However, they will also partake in other activities commonly associated with babies such as drinking from baby bottles and being wet-nursed. Adult babies also crawl on the floor, play with toys and eat baby food.
The condition often requires the individual in question to regress to an infant-like state. In some situations, the fetish can cross over with masochism where the individual in question likes not only being spanked but humiliated as well, all in an effort to achieve sexual arousal that the activities tend to elicit in people (most often men) prone to paraphilic infantilism.
The adult baby fetish is relatively recent, at least as far as medical records are concerned. Before the 1980's, there were only a handful of cases of adult baby syndrome that had been documented, this including one case of a man who would have to defecate in a diaper he wore under his clothes in order to reach an orgasm.
There are many variations of this particular fetish, and psychiatrists have only recently begun making more of an effort to understand the factors that drive the syndrome. Some medical experts have described the adult baby fetish as a branch of the sadomasochistic fetish where individuals seek to be dominated in some sense.
In the majority of cases, men, be it heterosexuals, bisexuals or homosexuals, simply wish to be treated like babies as a sexual role play. Certain studies have attempted to connect paraphilic infantilism to childhood sexual abuse and issues of sexual identity.
It should be noted, though, that in a number of the studies and surveys that have been carried out into the condition, the majority of adult babies are men in their late thirties, most of whom are not only well educated but often pursuing stable sexual relationships with their spouse.
There is no real consensus at the moment on the factors driving and eliciting paraphilic infantilism. It is also worth keeping in mind the fact that most adult babies do not consider their fetish to be a syndrome that requires treatment, especially considering the fact that the fetish doesn't actually impair their ability to function.