Should People with Allergies Use Dysport an Alternative to Botox?

If you're asking if patients who have never had botox or dysport, but have a history of being allergic to things, such as hay fever, asthma, antibitoics, etc. should try one over the other botulinum toxin, they are relatively similar but possibly less free protein load in Dysport.  If someone is truly allergic to Botox, possibly they wouldn't show a reaction to Dysport but Allergic reactions to Botox are so rare that most physicians have never seen such a reaction. If this is a possiblitiy with you, then you should see an allergist who can test you to the products if the physician who is about to inject you can supply the allergist with the chemicals. There is a chance that someone can become allergic to an ingredient in the liquid that the Botox or Dysport is mixed with prior to the injection.  This has to be investigated as well. Some doctors use preserved saline and the allergist may have to test this as well and then if this is the cause, botox mixed with preservative-free saline might not induce an allergy. If there is an immunologic reaction wtih antibodies, then changing to another serotype might make sense, but none exist now (dysport and botox are both serotype A botulinum toxin) and the prevalence of immunity to botox is extremely rare.

I have never seen an allergc reaction to either but would not use something if you have a KNOWN allergy to any of the ingredients. Better safe than sorry.

The answer here depends precisely on the nature of one's allergy.  Your question seems to be hypothetical.  Occasionally people without out allergies harbor the belief that it is a good idea to avoid drugs to which others have allergies.  If you do not have a known allergy to the ingredients of these agents, then it really does not matter which of these drugs you have.  If you have an actual allergy, I recommend that you consult your potential doctor.  You may actually need to be patch tested to determine if a product is safe for you.