Lena Dunham
Actress Lena Dunham arrives at the 71st annual Golden Globe Awards in Beverly Hills, California, Jan. 12, 2014. Reuters/Danny Moloshok

Lena Dunham, creator and star of HBO's hit series "Girls," said Monday she was taking time off from a press tour for season five because of a medical condition. Dunham announced her plan to rest in a social media post describing how she suffers from endometriosis, a condition common to women in their 30's and 40's that can cause sometime severe pelvic pain.

"I am currently going through a rough patch with the illness and my body (along with my amazing doctors) let me know, in no uncertain terms, that it's time to rest," Dunham, 29, wrote in an announcement to Facebook. The writer and actress had to cut her press tour for season five of the series short because of pain from the condition.

The disorder is very difficult to diagnose, but as many as 5 million women in the United States suffer from it, according to the National Institute of Health. It is a painful condition in which the tissue called endometrium that is supposed to line the inside of the uterus grows outside of the uterus, often on bowels, ovaries or in the pelvic region. When the tissue breaks down and bleeds, as happens during menstruation, it is trapped inside the pelvis, causing often extreme pain and scar tissue, according to the Mayo Clinic.

While endometrium growths are usually confined to the pelvic region, some people with the condition have seen the tissue grow inside their arms, legs and on other organs.

"I’m riddled with scar tissue, inside and out," wrote endometriosis sufferer Lorna-Jane Richardson in an editorial published in U.K. newspaper the Telegraph Tuesday. "My organs are stuck together with scars called adhesions," wrote Richardson, adding "I’ve had seven surgeries over the past eleven years and there will be more. I’ll never be bikini ready."

Doctors are uncertain of what causes the disease, and few treatments are available. Women who suffer from endometriosis often take oral contraceptives or other hormone treatments, and many have multiple surgeries to remove growth of the endometrium tissue.