A haircut might be *just* what you need.

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Kaley Cuoco has gone long again. Mid-hair extensions, she posted an Instagram pic and an explanation for her makeover—to celebrate the end of filming The Big Bang Theory.

“It’s very important for me to change my look after wrapping each season,” Cuoco wrote. “I love playing Penny, but it’s good for me to bring it back to Kaley.”

That familiar urge to mark a life transition with a physical transformation makes sense, because how you feel and how you look are so closely linked.

“A positive self-image can stimulate the reward center of our brain, so if we like the way we look, it can impact us emotionally, and help us feel better about more than just our appearance,” explains Vivian Diller, PhD, a psychologist in private practice in New York City who specializes in self-esteem, body image, and beauty.

Aside from milestones, here are three more instances when changing your appearance can be a healthy choice—and one time you may want to put away the box of hair dye.

When you feel uninspired

Maybe you’ve been in the same division at your company for a while now, and crave something fresh. Or you're in a long-term relationship and things are … stuck. “When we feel unmotivated at work, or our relationship seems dull, change can help bring some vitality to our lives,” says Diller, who wrote Face It: What Women Really Feel as Their Looks Change and What to Do About It ($16; amazon.com). Of course, chopping your hair isn’t going to solve your problems. But it can affect how you view your life, and provide some much-needed clarity, Diller says.

When you land a new gig

It can feel energizing to start anew with a different style, says Diller. But if you’re moving to a new role within your company, don't do anything too drastic, because a total makeover might give the wrong impression: “You don’t want to be viewed as trying to change things up too much,” she says.

When you’re getting over a bad breakup

No one’s suggesting that you run to the salon and go platinum. But a well-thought out, well-planned change may do you good. (See: “Revenge looks” by any celebrity post breakup. Ever.) “It’s important to deal with a breakup emotionally, but it doesn't hurt to move things along with changing up your look,” saysDiller. “It can help you leave behind bad memories or the associations with a past relationship,” she adds.

When everything’s changing

Maybe you’re pregnant. Or your company is relocating you across the country. These are times to proceed with caution. Big changes that create a good deal of upheaval in your life are not when you want to go wild at the salon, says Diller. Rather, "it can help to keep other things constant, including your look," she explains.  "Maintaining stability can give us the wherewithal to deal with dramatic life changes.” Besides, we don’t have to tell you that you look beautiful just the way you are.