Who tends to get serious allergic reactions to aspirin? Is it almost always people w asthma or nasal polyps or can anyone suddenly have a problem?

No. It does not always involve asthma although nasal polyps and sinusitis often precede the onset of asthma in aspirin-sensitivity. This is a condition usually found around ages 30 on the average. Yes it can develop all of a sudden.

Related Questions

No nasal polyps, no asthma, but 3 or 4 hives after nsaids. Also some tiny hives with no nsaids at times. I want to take aspirin anyway. Safe enough?

Which NSAID? Hives from NSAID is considered to be an allergic reaction specific to that nsaid. Although once suspected to worsen hives from any cause, this is no longer true. However if your hives occur in the absence of nsaid, then it is likely from causes other than NSAID including asa. Thus you will need to sort out which NSAID you need to avoid (read the generic not the brand name).