What causes Botox injection to cause severe burning and pain?

There are times when your body is more sensitive to injections, especially in times of stress.  The other cause for the pain is that some other dilutant other than sterile salt water was used.  I would contact the office where you had the injections and inquire with them.

When Botox was approved the instructions were to mix it with saline. Physicians that use this often quickly learned that using bacteriostatic saline removed the sting from  the injections. The portion of the saline that makes it bacteriostatic also keeps it from stinging. If your Botox was not mixed with this it probably did sting.