[2][better source needed] Karp's infant calming technique is supposed to be based on recreating elements of life in the womb.

[8] Karp calls the ingredients of his method for soothing young babies the "5 S's": tight swaddling, side/stomach position, shushing, swinging and sucking.

Lactation and breastfeeding expert Nancy Mohrbacher collected several scientific studies which demonstrated negative aspects of swaddling on newborn infants.

[17] In 2010, researchers studied the effects of video instruction concerning swaddling, side positioning, white noise, jiggling, and sucking on parents' ability to calm fussing babies.

[18] CBS news reports that "Critics say Karp is riding to fame on the strength of his patients' VIP parents, who include Michelle Pfeiffer, Pierce Brosnan and Madonna.

"[19] Part of the appeal of Karp’s methods for calming babies was that it didn't require any fancy or expensive equipment beyond a blanket.

A New York Times article documented how his messaging changed with the creation of the Snoo toward spending money on the device: "Now he was suggesting that, actually, the best way to improve your baby’s sleep required splurging on a sensory bed.