For most people, cold weather is an inconvenience, requiring an extra layer of clothing or the thermostat to be turned up. For others, exposure to cold can trigger an allergic reaction severe enough to cause them to collapse.
Cold urticaria is a rare but potentially dangerous condition in which contact with cold temperatures causes the immune system to misfire. The results can be hives, swelling, pain, and in some cases, life-threatening anaphylaxis.
The condition was first described in 1792 by a German physician called Johann Peter Frank. Today, we know it is almost twice as common in women than in men, with the average age of onset in the early twenties, though it can affect people at any age.
There is some good news: between 24% and 50% of people with the condition see improvement – or even full recovery – over the years.
Aside from a few very rare genetic causes, why some people develop primary cold urticaria remains unknown. What is clear is that mast cells are involved. These sentinel cells act as first responders in the body's tissues – including the skin – alerting the immune system to danger signals or germs.
When mast cells are activated, they release a chemical called histamine. Think of histamine as an alarm that alerts other immune cells to rush to the area. It also makes the blood vessels in that part of your body widen and become "leakier", which causes the telltale swelling, redness, and itchiness.
Normally, this response is helpful – the extra blood flow and leaky blood vessels allow immune cells to squeeze out of the bloodstream and into the surrounding tissue to fight off a genuine threat. But in cold urticaria, it's a false alarm. Your body is mounting a full-scale immune response when there's nothing to fight, causing discomfort without any benefit.
Doctors test for cold urticaria by placing an ice cube on a patient's forearm and watching what happens after they remove it. This test typically follows patients noticing they develop welts, hives, or rashes on exposure to cold things. This must be done by a medical professional because in about 20% of cases, it can trigger anaphylaxis.
As winter continues, it's worth remembering that for some people, the cold isn't just uncomfortable – it can be genuinely dangerous. Understanding and recognising cold urticaria could make all the difference.