Siblings fight, sometimes a lot; there is nothing new about that. In fact most parents would consider this pretty normal.

But a new study released by the American Academy of Pediatrics shows that being picked on by a brother or sister can be harmful to a child’s mental health, resulting in increased anger, depression and anxiety in the victimized child.

Kirsten Reddish, a counselor with Youth Eastside Services, has worked with families where sibling bullying is a big problem.

“Since it’s often an older sibling picking on a younger one, the younger child is at a disadvantage because he or she doesn’t have the skills to deflect the aggression or express what’s going on—except to act out, often in ways that aren’t helpful,” she said.

Sometimes what is essentially teasing can rise to emotional abuse. The abused sibling can become frustrated at not being able to keep up in the verbal volleying. Some may resort to throwing something or becoming physical. In this way it can quickly escalate to physical abuse.

Because identity formation is a big part of ‘tween and teen years, bullying can shape a child’s self-image. Children who are bullied often take on a victim mentality that makes them feel “less than” the sibling doing the bullying. This can really deflate self-esteem.

In one case noted by Reddish, the child’s victim mentality made her a target at school as well.

“She became hopeless and had fantasies of harming her older sibling,” she said.

Conversely, sibling relationships that are close and nurturing have been found to play an important role in developing a child’s ability to relate to peers and resolve conflict, as well as his or her social and emotional intelligence.

In the study, researchers interviewed more than 3,500 kids under the age of 17 (or their parents). They assessed the range and extent of sibling aggression, looking at measures like physical assault, with and without a weapon or injury; property aggression like stealing something from the child with or without force, or breaking a sibling’s things on purpose; and psychological bullying such as saying things to make the child feel bad, scared or not wanted. Mental health was also assessed.

The results showed that sibling aggression was associated with significantly worse mental health and distress was evident even in cases of mild sibling aggression. The data also found that sibling and peer bullying had very similar negative effects on mental wellbeing.

“I think the important thing to take from this is that parents, and those who work with children, should treat sibling aggression as potentially harmful and not dismiss it as normal,” says Reddish.

It can take time for parents to distinguish between normal sibling arguing and aggression or bullying behavior — after all, some kids have a short fuse, especially if there are other stresses at home or in school. Things to watch for include a child who sees himself as less than others, or one sibling who always seems at fault while the other is usually the “good kid.”

Reddish recommends working with the perceived “victim” and helping the child express how certain words or actions make her or him feel. The more concrete a child can be at verbalizing, the better he or she will be at resolving conflict.

“Ask about the sibling and how they perceive their relationship. Who is stronger? What they do when their sibling hurts their feelings? Does that work?” says Reddish.

It’s also beneficial to let the aggressive sibling understand how words or actions impact or hurt a brother or sister. And when there is trouble or an argument, give consequences to every child who was involved.

Finally, one of the biggest things parents can do is look out for how they model relationships. If there is a lot of contempt between partners or ex-partners it can cause a child to see hurtful conflict as a normal part of relationships.

As always, if the situation seems serious or you are unable to improve it, reach out for help from a child counselor, such as the experts found at Youth Eastside Services.

Patti Skelton McGougan is the executive director of Youth Eastside Services.