Aging and illness can worsen a person's negative personality traits, says clinical psychologist Mary A. Languirand on AgingCare.com, pointing out that major changes and fear of the future are usually the driving factors behind the bitterness. Your parent's negativity may be a reaction to the changes that come with growing older, such as uncertainty about her health or a loss of independence. She may be feeling that her quality of life has lessened due to losing touch with friends, not being able to make money, not feeling useful or needed by her loved ones or being crippled by an illness. These negative emotions may then be expressed as bitterness toward her situation.

Your parent may be going through a tough time, but that doesn't mean you have to put up with his negative attitude. Create boundaries to keep yourself sane and to prevent the build up of resentment that comes with feeling disrespected or unappreciated. Confront your father about his bitter attitude, be open about how it is affecting you and let him know what kind of behavior you will not accept. Be assertive, but respectful. Your parent may respond positively to the word "no," because it indicates that you will not treat him like a baby. He may also not have realized that he was taking his frustrations out on you because he was too wrapped up in his own issues. Even if he responds with more bitterness, remember that creating and enforcing boundaries is necessary for the relationship to be healthy, according to gerontologists Barbara Silverstone and Helen Kandel Hyman in "You and Your Aging Parent : A Family Guide to Emotional, Social, Health, and Financial Problems."

You may not be able to change your parent's negativity, but you can control how you react to it. If your mother is on a negative rant, try redirecting the conversation to a more positive slant. If that fails, learn to block out what she is saying, in the same way that young children learn to block out their parents' nagging, suggests therapist Reneau Z. Peurifoy in "Anxiety, Phobias, and Panic." This is a defense mechanism that may require practice. Another technique Peurifoy suggests is to visualize a fence or a force field protecting you from her bitterness and negativity. After spending time with a bitter aging parent, you may be emotionally drained, so do something that counters that negativity. For example, relaxation techniques like meditation, yoga, reading or praying might help.

If your parent's bitterness is taking a toll on your mental health, you may need to make some changes to take care of yourself. For example, try shortening the length of your visits, but increasing the amount of times you visit. Instead of seeing your father once a week for six hours, seeing him every other day for an hour and a half will have less of a negative impact on you, says Peurifoy. If you can, try setting up a family therapy session, suggests Languirand. This can help you work toward understanding each other better. If your parent refuses, attend therapy sessions alone for a place to freely express your feelings and practice ways to deal with specific situations.