Serena and Blair, Kyle and Cartman, the Heathers or half the cast of the “Real Housewives.” What do they all have in common? They’re examples of toxic friendships—they’re frenemies.Positive friendships can make you more beautiful. Study after study show that strong social networks are super important for lasting health and wellbeing. But when a friendship takes a nasty turn? It can seriously stress you out.A frenemy is a portmanteau word that combines “friend” and “enemy,” and is symbolic of the kind of love-hate relationship some women know all too well.“There are lots of different classes of relationships that we have with people in the world,” says Art Markman, Ph.D., a psychology professor at University of Texas at Austin and YouBeauty Psychology Advisor. There are market relationships (you pay the cashier for your groceries) and neighborly ones (the guy next door jumpstarts your car; you bake him cookies to say thanks).“With close friends and family, you enter into this communal relationship in which you do things for your friends, and they for you,” he says. “In an ideal world, you’re not really keeping track. If something happens, you know your friend will be there for you.”Identifying a Toxic FriendshipSometimes a friendship is less than ideal. Turns out, your friend isn’t there for you—or she undermines you, blurts out your secrets, takes teasing a little too far, steps out with your boyfriend or talks behind your back. That’s when things can turn toxic. “You begin to realize that your friend is not playing by the same rules that you are,” Dr. Markman says. “You were treating her as a friend, and she’s not sharing in the same way.”RELATED RESEARCH: Women Tend to Exclude OthersEleanor May*, 36, a social work graduate student in New York City, had been friends for about eight months with a woman we’ll call… Brandy. “We were both laid off at the same time,” says May, “and we began spending a lot of time together—like every day.” In the beginning it was fun, but then May decided to apply to grad school. “Brandy was still in this Oh-I-don’t-have-any-idea-what’s-next phase. I think that’s where a jealous thing was happening. And she turned very mean, very quickly.” While helping May fill out applications, Brandy started bad-mouthing her behind her back to mutual friends, doubting that she’d get accepted anywhere.“As friends, you are on the same team. You are part of the same tribe, if not the same family,” says Dr. Markman. “When you draw your mental lines in the world, if it came down to us vs. them, who’s the ‘us?’ Your friends are part of the ‘us.’ There may be a relationship with good-natured teasing, but when push comes to shove, you want to believe your friend has your best interests at heart.” What to Do About FrenemiesWhen this belief is challenged (because your friend throws you under the bus at every opportunity), you may find yourself going over and over interactions, wondering what’s going on, says Laura B. Fortgang, a career and life coach and author of “Living Your Best Life.” “If you walk away from someone who’s supposed to be your friend, and you are venting and gossiping about them,” she says, “there’s something they did that crossed your boundaries, and something you didn’t say.” Her advice would be to ask yourself what you wanted to say, and why you were afraid to say it. “It’s not bad to look at yourself first,” she says.But sometimes you’re not the problem. Brandy’s trash talk eventually got back to May. “I was completely hurt by everything,” May says, and she started spending less and less time with Brandy.“When you recognize that there’s a problem in the friendship,” says Dr. Markman, “that’s really the point at which you have to be willing to communicate. The worst thing you can end up doing is holding that feeling in. For one thing, you may have misinterpreted something.” If a simple conversation might save a friendship, you owe it to that friendship to at least try.Fortgang agrees that communication is key. “You have to ask yourself, ‘How do I renegotiate this friendship?” she says. “That’s going to be the first step to perhaps shifting that relationship.”Brandy figured out that May was avoiding her. “Then I told her all the things I’d heard. She admitted it all,” May says, but she got no apology. “This is just her personality. I’ve seen her do this to other people.”In some cases, the only solution can be to end the friendship, Fortgang says. Where there’s abuse—lying, stealing, undermining—“big problems like these might require a complete break in the relationship,” she says.Toxic Friendships Damage Your HealthOther than saving yourself some aggravation, what’s the reason to trade a toxic friendship for a more positive, nurturing one? The answer is that it just might save your life. Most people think of toxicity in friendships as being metaphorical. Bad friendships can, however, be toxic—literally.MORE: Are Bad Habits Contagious? A meta-analysis published in the journal PLoS Medicine found that people with stronger social relationships had a 50 percent higher likelihood of survival (in the period studied) than people with weaker relationships. Comparing the results of 148 studies (involving 308,849 participants), the Brigham Young University researchers found that low levels of social interaction were as or more harmful than other serious health risks, such as obesity.In another study published in the journal Hormones and Behavior, bonding with friends raised progesterone levels in women, a hormone that’s linked to more sociability and willingness to help out—behaviors that reduce stress and anxiety.Welcoming good friendships into your life could possibly save your life—or at least make it a whole lot more relaxing and fun—when you say ta-ta to toxic.*Names have been changed.