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.