It is called Golfers Vasculitis. I had it this past May when we did 2 parks in one day. Neither were MK.
Causes of the Heat Leg Rash
Researchers interviewed several people with the rash and discovered that many underwent extensive allergy testing because they believed they must have been having a reaction to some chemical or plant. But it was simply an irritation of the blood vessels following prolonged exercise in the heat, such as walking for extended periods or playing 18 holes of golf.
The rash is more common in people over 50. Most walkers can't pinpoint anything new they have used that may be causing a reaction. And since so many walkers have it, they couldn't all have contacted the same irritant. The source is simply heat and age--your leg blood vessels getting irritated from the heat.
Prevention and Treatment of Golfer's Vasculitis
The research offered no treatment or prevention recommendations.
It seems to occur in healthy, active people. The researchers suggest it should not be a health concern and recommend not getting allergy testing, etc.
In my non-medical experience at
Breast Cancer 3-Day Walks and walking conventions, this rash appears on a vast range of walkers and commonly goes away by itself after a few days. Pampering yourself after a good long walk by taking a cool bath, sitting with your feet up, or applying cool wet towels to the rash may help relieve discomfort.
Other Heat Rashes
Heat Rash - Prickly Heat
Unlike golfer's vasculitis, prickly heat is itchy. It is triggered by blocked sweat glands and causes raised itchy red dots or bumps. It is best treated by getting out of the heat for a few days and not scratching the area.
Heat Rash and Prickly Heat