Social networks promote jealousy. No matter how much people try to not compare themselves to others, they still do it and as a result they feel bad when they check the news of the people they follow. See why people become jealous.
Instagram filters make people look much more attractive than they truly are. Even if you know how someone looks in real life your subconscious mind will still be fooled by the pictures. You can start getting attracted to a person as a result of this deception. See why do people lie to themselves .
Because Instagram pictures usually provide more sensitive information about you than Facebook pictures, your followers can get to know fine details about you and your stalkers can easily get information they are looking for.
Even if you have loving and caring friends you can shortly feel unpopular after checking Instagram. When your pictures get 5 likes and someone else's gets 200 likes you will unconsciously compare yourself to that person and feel bad. See also why Instagram is so popular.
On Instagram everyone pretends to be living an awesome life. The fact that you won't be able to tell whether people are pretending or not can make you feel miserable since you will always compare your life to the wonderful lives those people are living.
Because it's easily accessible (one tap and you are in) Instagram can be very addictive since many people turn to it when they are bored. The fact that a social network that promotes bad moods is also addictive makes it very bad. See Why Mark Zuckerberg bought Instagram for $1 Billion dollars.
Studies have shown that irrelevant data can be very annoying to the brain. If you hate sushi or are not interested in food and you saw someone posting his sushi plate on Instagram, there is a very big possibility that your mood will change to the worse. See also why Facebook is so negative.
On Facebook most of your friends will add you but because of the word 'follower' people's Egos can prevent many of them from following you. As a result you might have a small number of followers and in turn a small number of likes.
At any point a person can easily unfollow you, leaving you to your self doubts. While on Facebook it's very rare for someone to delete a friend, on Instagram people unfollow others a lot. See also why Instagram filters are bad.
Instagram is all about people showing off their looks. If you don't look good in pictures, there is a great possibility that Instagram will ruin your self esteem as you compare your looks to others.
If you were lucky to get many fans, there is a high chance that Instagram can turn you into a narcissist. See Why Celebrities like Instagram.
Instagram can contain inappropriate pictures that kids shouldn't see. Because people share more intimate pictures on Instagram, it might not be a good idea to let a kid have an Instagram account .
Many people use Instagram to broadcast a fake life style that they are not living or to show that they are always happy where as this could be very incorrect. See also why Instagram is so fake.