Does letting a baby “cry it out” have harmful effects on the baby in the long run?

If parents are taking "cry it out" much too literally and ignore their baby for hours on end, that is neglect and absolutely has a negative impact on infant development. However if they are doing CIO in the correct "extinguished crying" method, there are no negative impacts because the baby is not being ignored or neglected. He or she is simply being allowed the opportunity to self-settle, and the parent is always listening close by. If after a limited interval of time baby is either crying or the crying escalates, the parent goes to their baby and attends to their needs. 

baby's have enormous stomach pain gluten and water is poise for them

If you consistantly and constantly ignore a baby every time  it needs comfort it can actually do harm to their emotional growth, BUT~~ letting a baby have a cry for a few minutes once in a while will not do any harm, and will actually encourage the baby to learn how to self-soothe, which they will need to learn in order to take care of their own needs. 

I used to always let my baby cry it out, every night at 5pm she would start! This was from about 10 weeks old; went on for months. Dr said it was colic. I would put her to bed and watch on the baby monitor from another room. Nothing I could do would console her. She out grew it. She’s 12 now and she’s absolutely fine and doesn’t even remember the stress she used to cause me 

Doing it RIGHT does no harm.

Doing it wrong can cause all kinds of problems.

Parents sometimes start trying this on babies that are too young for it.

Parents sometimes let the baby cry for too long before offering some soothing assistance.  

"Crying it out" is all about HELPING the baby learn to soothe themselves and some parents forget about the "helping" part.

Depends on WHY they are crying most times it's O.K they learn to self soothe just make sure they are not injured, dirty and wet, or hungry....

N.Shadows

Absolutely!  That's why people cry after the age of 2.  Use the pillow technique. 

sometimes they cry so hard they get hernias. try that baby rocker that vibrates. or a plush toy that vibrates. that motion is very calming.