Surprisingly enough, the allergic reaction mainly developed on the shirt-covered skin.
In conversions then I learned that the shirts were cleaned with the economical and energy-saving quick wash cycle (20 min, 30 °C). This involves less rinsing cycles with the consequence that detergent residues still can be left in the laundry. This especially applies to non-tensidic perfume substances and antibacterial preservatives. The culprit in this case was methylisothiazolinone, banned only recently for cosmetic leave-on products but still widely used in laundry detergents.
Bottom line is that the initially suspected sun allergy turned out to be a contact allergy to methylisothiazolinone which was intensified by heat and sweat. The substance was properly labelled on the packaging of the laundry detergent though.
Hint: The amount of preservatives left in the textiles after rinsing depends on the type of tissue (cotton, nylon, polyester etc.). A good advice is not to economize on rinsing cycles if the laundry detergent contains such components!
Dr. Hans Lautenschläger