I have eaten seafood all my life (33yrs), 99% of the time without incident.
I had medium severity asthma and atopic eczema as a child, both of which lessened considerably as I got older, becoming non-problematic since I was about 15. I still get the odd flare-up of eczema, usually in Spring, and my asthma management has for a long time consisted of using my ventolin inhaler about 3-5 times a year.
12 years ago I had a large seafood platter (fish, molluscs, crustaceans) at a restaurant, and a few hours later, I awoke with an in-progress asthma attack, very puffy swollen face, and extreme nasal congestion. I had an uncomfortable night, but by early morning, the symptoms had mostly disappeared.
And then last night, after enjoying a home-cooked seafood pasta, I again awoke a few hours later with the same symptoms as described above -- this time with some chest pain, swelling in the hands, and a lot of itchiness in the hand creases. Again, after being awake all night, the symptoms had mostly disappeared by morning.
The only other seafood-allergy related incident I can recall is a cooked japanese lunch meal I had about 6 years ago (the only seafood was squid I believe), where I experienced double-vision for a couple of hours after eating.
Other than this, I would say I have eaten seafood (all types) at least twice a month for my entire life, and these are the only incidents I have experienced.
Given what I have read on the internet, seafood allergies do not behave this way. You either have an allergy to a particular type of seafood, and eating that type of seafood triggers the allergy in virtually 100% of cases. I clearly do not have this type of allergy.
Can anyone shed any light on this?