I have concluded ...

 ... that No Mow May* and a grass pollen allergy may not be entirely compatible.

I had lunch on the patio, which is right next to a patch of knee high grass at the 'flowering' stage. I enjoyed lunch, but it's four hours later and even after a bath and a complete change of clothes my skin is still crawling.

I suspect the bottom half of the lawn is getting mown tomorrow

* The idea is not to mow your lawn in May to encourage biodiversity, and it works, I had a couple of rare orchids show up last year, but no sign of them this year. They were in the top half of the lawn, which I'm planning to leave unmown.