The girl who's allergic to everything

21-year-old Brynn Duncan has spent much of her life in a virtual bubble. The young woman from South Carolina has a rare disease that leaves her vulnerable to suffering potentially lethal reactions to a seemingly endless list of allergens. For years, she got sicker and sicker, experiencing problems with an ever-increasing list of foods, and doctors couldn't figure out what was wrong.

Finally, as she writes on her blog Brynn's Bubble, "After seven years of searching for answers, I was diagnosed with Mast Cell Disease and POTS (Postural Orthostatic Tachycardia Syndrome) in 2012."

Mast Cell Disease, or mastocytosis, is a rare condition that occurs when the body produces too many mast cells, a type of cell essential to the functioning of the immune system. The National Institute of Allergy and Infectious Diseases explains that the symptoms can include typical allergic responses such as itching, flushing, abdominal cramping, and in serious cases, shock. In addition, patients may experience muscle and bone pain, abdominal pain, nausea, vomiting, diarrhea, and ulcers.

In Brynn's case the allergic reactions became so severe, and the triggers so pervasive, that she was put on a feeding tube for nutrition and receives Benadryl through a pump around the clock.

She says her other diagnosis, POTS, "causes my blood pressure to drop and heart rate to skyrocket upon change in position. To put it in simpler terms, POTS causes me to pass out if I stand for more than a few minutes at a time."

After a difficult year marked by multiple surgeries and months in the hospital, Brynn writes, "I never imagined that I would be able to make a comeback. At the beginning of 2014 I couldn't even stand without assistance from a walker or leg braces- Today I can walk up the stairs without thinking twice about it."

On her blog, Brynn reflects on how the health challenges have shaped her life -- even finding some good in the struggle. "One of the parts that I appreciate the most about living with a chronic illness and having so many close friends with chronic illnesses- I don't leave words left unsaid. I tell my friends that I love them every chance I get because in the back of my mind I always ask myself if I would be happy with my words if they were to be the last words to a dear friend."