Why is mustard irritating for me?
As a straight answer to "why" it's the quantity of mustard oil in any given mustard type.

There are many types of mustard, but the two you may find the most confusing visually are English &amp; American.

Though both are a fairly bright yellow in colour, that's about as far as the similarity goes.

Mustard seeds themselves come in many different 'heats' - the mildest generally being pale yellow, almost white &amp; the strongest are dark brown.
Additionally, mixing mustard with vinegar tempers the heat &amp; lengthens the shelf-life.
Mixing instead with pure water increases the punch, but the flavours will dissipate over a much shorter period.

American mustard is one of the mildest available. It starts with a mild seed, pale yellow/white in colour, but the colour is then boosted by using turmeric. The mixture is then diluted with vinegar.
This is your 'standard' mild American mustard, found in many places, including McDonald's. You can slather it in huge quantities on a hot dog with no ill-effects.

Almost at the other end of the scale [Chinese mustard can be even hotter] is English. Made with a mixture of yellow &amp; brown mustard seed, then mixed with water not vinegar, this will take the roof of your nose out if used in injudicious quantities. It can quite literally make your eyes water &amp; your nose run - though if you did it by accident, take solace in the fact that the hit is very short-lived, not like eating a blindingly hot chilli pepper.
The full impact &amp; flavour of English mustard is quite short-lived even in the jar, once made up from powdered mustard. Even ready-made, store-bought has quite a short shelf-life for a condiment.  Made at home &amp; mixed with water it will lose its punch in just a few days, so the trick is to buy powder &amp; mix it just 15 minutes before you eat it, for the full experience.

If you're ever uncertain visually which you are about to add - taste it first.

Personally I love English mustard on hot dogs! With ketchup too [one of the only things I will ever put ketchup on]. The balance between the sweet, vinegary ketchup &amp; the hard hit of the mustard is really quite the feast. Bring on the junk food!

There is an in-depth article on the various types at Serious Eats - Mustard Manual: Your Guide to Mustard Varieties