It's a possible allergic reaction arising from when the skin gets pierced or bitten by mosquitoes or mites. It causes itchiness or pain or other suchlike symptoms.That is an insect bite.
Yuugumo-neesan!
Did you get bitten on your neck!?
Wha—!?
Oh...
You mean th—
Right, right!
An insect bite, uh-huh!?
