Perhaps the main source of potential stress in the relationship is a daughter-in-law's fear that her mother-in-law disapproves of her in some way, according to research from Dr. Terri Apter, author of "What Do You Want From Me? Learning to Get Along With In Laws." That might mean recoiling at her mother-in-law's parenting advice, offer to help cook ("She doesn't think I can cook?"), or questions about life choices ("She thinks I'm wasting my time staying home with my kids and should go back to work"). In all of these cases, the daughter-in-law feels that her mother-in-law is judging her, particularly for her ability to take care of her own husband (and kids). This feeling of resentment can occur even though the mother-in-law may view these discussions as an attempt to become closer with her daughter-in-law or to help her make the "right" choices -- the ones that will make her the happiest.

Many women are protective over their own households, and view offers of help from outsiders as unwanted intrusions. Although the woman's own mother might be able to offer assistance, a mother-in-law does not have that same relationship. In addition, a mother-in-law who does not respect boundaries sufficiently might call too early in the morning or too late at night, might expect her son to help her change a light bulb or mow the lawn or might discipline her grandchildren in front of their mother. All of these acts of intrusion can strain the relationship, says Apter. It is important for the daughter-in-law to set clear boundaries, and for the mother-in-law to tread carefully, to ensure that the issue of intrusion does not become an problem in their relationship.

Beneath the external problems of boundaries and criticisms, the underlying stress that fills many in-law relationships revolves around the man who is at once a husband and a son. When a woman's son gets married, she may wonder how her relationship with him will change. The truth is, it will, and it should. Her son should stand by his new wife's side, even against his mother, although he should make sure that his mother knows that she is still an important part of his life. When he fails to do so, he can unwittingly create a battleground between his mother and his wife, where both try to subconsciously prove that he loves them best, says Apter.

Our society paints in-law relationships as inherently troublesome, says Sylvia L. Mikucki-Enyart, a researcher at University of Wisconsin-Stevens Point. Because mothers- and daughters-in-law often go into a relationship with the expectation that it will be tension-filled, they're more likely to walk on eggshells around each other and eventually become resentful about their relationship. This self-fulfilling prophesy prevents their relationship from starting off naturally, and could play a large role in their dissatisfaction with each other even years later.