Toddler with food allergy

most likely the immune system is just over reactive due to infection.

its pretty common for people to develop new food sensitivities with lyme etc

i would think it best to avoid the things you suspect a reaction to for now - it may well calm down again as treatment progresses and especially if given a rest

Strawberries, reishi, and red pepper are not generally considered to be trigger foods for MCAS. Some people even take reishi to help manage histamine. The strawberries and red pepper could trigger MCAS if they were very over-ripe (fermenting) or if they were cooked and left out for a long time (leftovers). The vitamin C could trigger a histamine response if it has citrus ingredients.

Considering MCAS is a good idea with sudden rashes and hives appearing, for sure, but I would assume you're seeing allergies unless he's having other MCAS symptoms (digestive, respiratory, fatigue, anxiety, nerve pain, etc.) and/or more typical MCAS triggers. A RAST food allergies blood test often is covered by insurance, if you think that might help you figure out what's going on.

Typical MCAS trigger foods might be: yogurt, miso, nutritional yeast, anything fermented, vinegar, some probiotics, lion's mane mushroom, alcohol, citrus, pineapple, over-ripe bananas, tomatoes, aged cheeses, aged meats, leftovers, etc. "High-histamine foods" can mean that something contains a lot of histamine or that something makes your body release extra histamine. Not everyone reacts to the same things. Fermented foods and ripe bananas ruin me, but citrus and tomatoes are fine.

I hope he isn't too bothered by these reactions! Poor kiddo.

MCAS or histamine intolerance (or both) could be going on. Here's a helpful clarification: https://mastcell360.com/histamine-intolerance-vs-mast-cell-activation-syndrome/

It's hard to know exactly what's going on, of course, but with Lyme what seems to happen most, based on what I have encountered, is that the body is over-reactive in multiple ways - inflammation, nerve signals, mast cells, etc. So there's a good chance that as his immune system heals and pathogen load decreases, he's likely to stop having these reactions. But they should be avoided as much as possible.

With a person so little, it does make sense to be cautious, in case these reactions escalate to something dangerous like anaphylaxis, and in case the system's increased stress load wears him down over time. It sounds like the reactions are increasing in number rapidly. I don't know how safe various mast cell stabilizer supplements and meds are for toddler-size humans, and in what dosages, but I know it's also probably hard to find a Lyme-literate, MCAS-literate doctor who sees kids! So maybe starting with a low-histamine diet is best, in the mean time? That's what has made the most difference for me.