A baby usually shrieks only when Grandpa (who is supposed to be helping you with a down payment on a house) or your boss (who is considering you for a promotion) tries to pick up the baby! (Just kidding.) Stranger anxiety, as this reaction is called, can actually set in at any age, though it usually hits full force when a baby starts crawling. Even a baby as young as two or three months may cry when a stranger picks him up — perhaps because he can sense that the stranger is nervous about holding him or because the stranger has an unfamiliar smell. When a baby of any age cries in someone else's arms, it is usually because he has formed a strong, healthy attachment to his primary caregivers. He can distinguish them from other people and he associates his well-being with them, whereas he does not know what kind of treatment to expect from a stranger. After all, how would you feel if someone you had never seen before picked you up and hugged you?
Once a baby can crawl or walk on his own, he may become particularly clingy and fussy and may show a more marked fear of strangers. While some babies only frown, pout, or bury their heads when strangers enter the room or try to hold them, other babies at this age will shriek terribly, with tears running down their cheeks, as if in horrible pain. The severity of the baby's reaction depends on his temperament in general and his mood at that particular moment, but researchers believe that a mobile baby shows more stranger anxiety because he is frightened by the new understanding that he can separate from his parent. A baby at this age also understands object permanence — he knows that his parent is somewhere, even if not in the room — and he cries when left with strangers as if to signal the alarm about the imposter.
Adapted with permission from "Why Babies Do That: Baffling Baby Behavior Explained," by Jennifer Margulis, published by Willow Creek Press. 2005 by Jennifer Margulis. All rights reserved.