I forgot to add that it's also not white in the centre the whole thing is red. From far away it looks like a perfect red circular area about the size of a dime
sounds like Phsoriasis or something similar, I have the same on my scalp and am trying to find out what the cause is ..no lice just dry itchy, scabby scalpyou described it well, mine started after I went out in the rain and my head got wet.
PS I live in the desert in CA so the dryness may not have helped till we got rain
While you did not report a tick on you, and I'd think it rather uncommon for one to dislodge on it's own, you do mention working outdoors and "bullseye" is a common term used to describe a Lyme infection site (though single rings occur also). Dime size is a bit small, but if it WAS knocked off...? Anyway - hope I'm completely off-base and that your symptoms have resolved/been treated successfully!