Jealousy happens most commonly within a romantic relationship, although it can occur between siblings and other family members, in friendships and in professional relationships.
A small amount of jealousy can be good. For example, if it's mild and well managed, it can help a couple to appreciate each other and add to the passion of a relationship.
But extreme jealousy can destroy relationships and damage your health.
Signs of jealousy
When someone feels jealous, they feel that someone or a situation is threatening something they value highly, especially a relationship.
Jealousy can make you feel angry, anxious and threatened. You might become hypervigilant, oversensitive and possessive.
When is jealousy a problem?
Clinical psychologist Linda Blair suggests that if you're concerned about your jealousy, ask yourself three simple questions:
1) Is this feeling interfering with my normal life?
2) Is my jealousy hurting someone I love?
3) Does my jealousy control me more than I control it?
"If the answer is yes to any of these questions, then seek help through your GP," says Linda. A GP can refer you to a counsellor or a therapist if you need further help.
In some areas you can refer yourself to your local psychological therapies team.
How jealousy can be harmful
Jealousy can take over your life and lead to sleeping problems and a poor appetite.
Linda says that intense feelings of jealousy can have similar effects to chronic anxiety, including a raised heart rate, sweating and exhaustion.
If not addressed, jealousy can also lead to depression.
Jealousy can affect your relationship in a negative way, especially if the perceived threat is not genuine and your partner is not doing anything to cause the jealousy.
Even the most devoted partner can feel hurt, exhausted, anxious and angry that they're not trusted. Ultimately, it drains them emotionally.
How to deal with jealousy
There are some practical and positive things you can do to overcome your jealousy. Linda Blair offers the following advice:
Talk to your partner
Tell them about your feelings without blaming them. Let them know what makes you feel worried and jealous.
Prepare what you want to say, and talk to your partner in a non-threatening, neutral atmosphere. "For example, arrange to meet in a café or restaurant. You'll be more likely to stay calm," says Linda.
Try to be objective
Just because you feel there is a threat, it doesn't mean that it's genuine. Try to view the situation objectively.
Accept some uncertainty
Uncertainty is a part of relationships. You can't ultimately control someone's feelings.
How a counsellor or therapist can help
A counsellor can help you to resolve your feelings of jealousy. They will help you look at the cause of your jealousy and deal with it on a day-to-day basis.
Linda says: "Knowing the origin of the problem is not enough to resolve it completely. You need to look at the everyday triggers, why you continue to feel and act that way. A counsellor or therapist will help you understand that."
Read more about the benefits of talking therapies.