What usually happens when a newborn smells vinegar, rotten eggs or ammonia?

Newborns have a sharp sense of smell. According to studies, newborns are attracted to pleasant smells and are repelled by unpleasant smells. For instance, when they smell chocolate or honey they exhibit a satisfied facial expression. On the other hand, they usually turn away or show a sad face when they smell ammonia, rotten eggs, or vinegar.