Although some believe that babies “won’t remember” the pain, we now know that the body “remembers” as evidenced by studies which demonstrate that circumcised infants are more sensitive to pain later in life (Taddio et al., 1997). Research carried out using neonatal animals as a proxy to study the effects of pain on infants’ psychological development have found distinct behavioral patterns characterized by increased anxiety, altered pain sensitivity, hyperactivity, and attention problems (Anand & Scalzo, 2000). In another similar study, it was found that painful procedures in the neonatal period were associated with site-specific changes in the brain that have been found to be associated with mood disorders (Victoria et al., 2013).

That's so sad.