Jellyfish sting - delayed reaction?

[Jenbot]

Two weeks ago in Cozumel, I took a hit from a jellyfish or something across the back of my hand. Immediate reaction, swelling, redness, pain, etc, lasted a couple of hours then faded away. But a week later back home the back of my hand erupted again in the same place with red welts that are taking days to fade away. Some research suggests that this is not unheard of. What I'm wondering is; first, is this a common occurence? And second, why does it happen? What would cause a reaction days after the initial sting?

I know this post is old, but I wanted to contribute because I got stung in Penang, Malaysia about two weeks ago (Feb 2024). I think the jellyfish was fairly small, and luckily I had some pain and welts for a few hours and by the end of the next day, all gone. However, one week later, it flared up again. I knew it was the sting because the pattern on my knee was distinctive. I have continued to get a mild flare up here and there, it is now two weeks later. Not painful, but a little itchy. Definitely a delayed reaction. I've been told that the poison is working it's way out, and it isn't uncomfortable overall, although it is a little unsightly. Hope this helps. ☺