The actress developed lymphedema, the buildup of fluid in soft tissues, which causes swelling in the arms and legs.
“I have a very mild case, but I have to wear compression garments from time to time, and it really does affect quality of life,” Bates, 67, tells PEOPLE.
At first, the American Horror Story star was angry about her diagnosis.
“I think sometimes you get depressed and think, ‘Why do I have to deal with this every day?’ ” she says. “I get angry about it and I get worn out with it and I get frustrated.”
But now, as an ambassador for the Lymphatic Education & Research Network [LE&RN], the Academy Award winner is hoping to spread awareness about the disease that affects up to 10 million Americans and can be “debilitating,” Bates says.
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“Now when I attend social events wearing my [compression] sleeves, I feel less self-conscious,” she says. “I want people to ask me about it.”
“Maybe if people can put my face on lymphedema,” she adds, “then more people will be willing to come out of the shadows and talk about it.”
For more on Kathy Bates, pick up this week’s issue of PEOPLE, on newsstands now
• With reporting by MICHELLE WARD TRAINOR