A British toddler recently suffered a life-threatening medical emergency called Stevens Johnson Syndrome, or SJS.

SJS is an autoimmune reaction, a situation in which the immune system, which normally protects the body from infection, misfires and attacks the patient’s body, treating it like an invading germ. Most people have heard of autoimmune disease like rheumatoid arthritis, in which the body attacks its own joints causing pain and swelling. But SJS is more rare than arthritis — and potentially much more dangerous.

In SJS, the body attacks its own skin. In the early stages, it can resemble other diseases, like the flu, delaying treatment. But SJS symptoms rapidly escalate to a painful rash with blisters, then sores and ulcers. The damage to the skin can cause permanent, disfiguring scars. And the disease can be lethal.

Two-year old Macey Marsh was prescribed Nurofen, an ibuprofen-based drug. Hours later, she was rushed to the hospital with the early SJS symptoms, including a rash with sores and mucus sealing her eyes. Physicians initially thought Marsh had scarlet fever and treated the reaction with antibiotics. The reaction got steadily worse until a physician realized what was really happening. Since SJS is so rare, physicians often assume it is a more common disease at first. Marsh was transferred to intensive care with pain so sever that doctors gave her morphine to control it.

For a time, Marsh’s condition was touch and go. Her parents were told to steel themselves for the worst case scenario. They were informed that even if Marsh survived, she could be blind. But the child rallied. After nine days she was able to see, but with some difficulty. A month after her initial reaction, she is recovering. Physicians continue to regularly monitor her condition.

SJS is nearly always triggered by drugs. But it is very difficult to anticipate what person will develop SJS from what drug. Many very common medications can trigger SJS in the right person.

SJS lawsuits allege that drug companies have not done enough to warn and protect the public from the risk of SJS and a related disorder called toxic epidermal necrolysis, or TEN. SJS lawsuits typically seek to recover the cost of medical care, lost wages, legal fees, and other expenses.