Even if you've never had the allergy before they can come on at random points in your life, if your still fine with the pre made liquid it might just be a case of some concentrates will irritate it while others are fine the same way as some people won't be able to taste most of a certain flavour but one concentrate on that flavour they can actually taste.

I don't have an allergy as far as I'm aware, but I find bready or cakey flavours catch in my throat and make me cough/hack when I vape. I'm guessing there's something in them that my body just doesn't like, no idea what, I just avoid them now.

You'll have to hunt around for a watermelon flavor that doesn't trigger you. Same thing happens to me with strawberry flavors - I've only found one that doesn't mess with me. Not allergic to strawberries, just the flavorings.

Yes, this has happened to a friend of mine. A few years back, we were trying to make a watermelon jolly rancher type flavor and every time she vaped it, her throat would get all weird and itchy. She is not allergic to watermelon or honeydew or any other kind of food at all. We never did quite nail down what the exact ingredient was, but we had three watermelon flavors - TPA Watermelon, TPA Watermelon Candy, and one that was from another company and was VG base. (Sorry can't recall exactly which one.)

She also once had a reaction to a honeydew e-liquid she bought in a store, but it was much milder. She did not notice it until she had been vaping it for a few days, unlike the watermelon reaction which was apparent within minutes. We always suspected they used a very small amount of watermelon flavor in the juice to amp up the "melon-ness" factor. She basically had to steer clear of any melon-based flavors after that.

I got the same issue with citrus flavors. So i guess yeah.

You can definitely be allergic to flavors. I've had pretty mild reactions and severe reactions.

As far as reacting to actual foods and flavors, it's complicated. I'm allergic to strawberry, but not strawberry flavors, artificial or real banana is an immediate reaction. I am allergic to melons and do react to melon flavored juices. I don't know that those two things are related, some reactions are due to proteins, some from flavor compounds, etc., allergies are complex reactions.

I've spent a lot of money on flavors that I can never use, unfortunately. It's a lot of trial and error.

I love watermelons and all the melons in real life; but, I cannot vape those flavors, they come off as so cloying that I actually get nauseous. Tank scrubbing flavors is what I call them, since the slightest hint if them makes me want to hurl.

Some citrus flavors in store bought juices give me a tickly feeling in my throat but since going diy, I've yet to have it happen and am wondering if it was bc of the percentages used in the mix, since I try to use as little flavor to get the desired effect in my recipe.

At the end if the day, diy is a process of trial and error that appeals to my curious nature. I have many flavors I bought and used once or twice, never to try again. It's a part of the process and should be expected. Good luck.

This is interesting, and never thought of this before. I seem to sneeze when I vape nic salts. Like have a lot of head congestion and sneeze all day, going back to a non nic salt non MTL I do just fine.

Could I be allergic to nic salts? Is that a thing?

I've had this same issue with doughnut flavors.