It was partly, he decided, the reaction of a healthy body to the contact with disease, and it was partly the tall grim Belsen chimney with its plume of innocent smoke.
But because of the delayed timing, it’s thought to be similar to a poison ivy reaction, which activates immune cells called helper and killer T cells and causes inflammation.
The population response to perceptible pollution may be pronounced when people have experienced a sharp increase in traffic and see the quality of their environment degraded.