u/Acceptable-Gap7024

Been having electrolysis sessions on my arms/shoulders the last twelve months. Never had an issue.
Started my back the other day and got this reaction four days after the treatment.
Any idea why, what I can do to prevent it and how I can calm it down? What is it and why did it take four days to turn out like this?
It was only a short session with roughly 250 hairs treated and it looks like a dozen or so follicles have reacted.