Great question — answering as the UphillTech team:
I am afraid this is the question to which you are unlikely to ever discover the answer. It is completely normal that you can smell some molecule that others cannot smell. When somebody smells an egg, several hundred compounds (of the thousands or more present in the egg) dock to receptors in their nose, and the combination of the information of these receptors, plus all other information available to the brain (including seeing an egg, being in a kitchen, etc.) leads to the recognition of an egg. And the set of receptors one has is pretty much unique to them. So, for everybody, there is a different subset of compounds their nose detects when they are around an egg. It so happens, that in an...
Full answer by rumtscho: https://cooking.stackexchange.com/a/120446 (CC BY-SA 4.0).
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