Hi L.,
Capsaicin is the active ingredient in hot peppers. That being said you may have had an allergic reaction or have a sensitivity to it. There are warnings about using capsaicin under certain circumstances like broken skin, skin irritation, hot pepper allergy, other drug allergies, reactions to dyes, foods, preservatives. Some say that you shouldn't use if you are breastfeeding or pregnant.
With a roll-on you may have simply used too much. There's not really a way to measure it. You didn't say why you were using it but I use a pain cream that not only alleviates muscle pain but heals as well. Let me know if you're interested.
Regards,
M.
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