Jealousy is defined as: resentment against a rival or resentment against a person enjoying success and advantages. It is also defined as fear of a rival. Jealousy is such an intense emotion that it can make a person feel anxious, sad, or angry. We may experience jealousy when someone appears to be more successful at a task than we are. Or we may feel jealous when a friend receives more praise than we do. People overcome by jealousy tend to be suspicious of potential "rivals."
The way people tend to "get back" at those they're envious about is by withholding commendation when it's well-deserved. They may think that's a way to stop someone else's success or acknowledgements, but they do not realize by doing this it is cheating oneself. All you're doing is creating unnecessary bile in your system towards someone that might not even be aware of your hostility or envy towards them - which means you're holding back your own happiness by holding this ill feeling on the inside. In the meantime you are losing out on each passing moment of happiness for as long as you remain this way.
I'm writing about this not because I'm an expert on the subject, but I've observed the effect it has had on those that are jealous of others.
Why should we care about all of this you ask?: Because of what medical reports have indicated. Reports indicate that anger and hostility can become triggers for strokes and heart attacks. Recently, a medical journal when speaking of people with heart disease compared explosive anger to poison. The journal also stated that "getting really mad can mean getting really sick." Think about that the next time you're feeling jealous...
My advice: be happy for others! If you admire them, commend them and you will find what you admire can become a part of you.