• Underarm burning pain has several possible causes."formal night" is Copyrighted by Flickr user: Rennett Stowe (Thomas) under the Creative Commons Attribution license.
  
  

Paresthesia

• Burning sensations in the skin are known as paresthesia. Any type of tingling, burning or numbness can indicate a damaged sensory nerve. Causes typically include a nerve injury or a disease affecting the nerves (one serious example is multiple sclerosis).
  
  

Chemical Problems

• The burning pain could be a result of the deodorant you're using. Some people are sensitive to the chemicals used in common deodorants. Try switching brands or going without deodorant for a few days to see if the pain subsides; a dermatologist can help you find a product that won't irritate your skin.
  
  

Cancer

• A burning or aching sensation in the underarm area can be a symptom of swollen nymph nodes or tumors in the breast. Do a breast self-exam and see your doctor right away if you find a lump.
  
  

Post-Surgery Problems

• If you've had surgery in the areas around your underarms (e,g., breast or shoulder), there could be scar tissue or a pinched nerve causing the pain. Check with your doctor.
  
  

Treatment

• If the problem is skin-deep (such as irritation from a chemical), your doctor can prescribe a cream to ease the pain. You probably won't be able to wear deodorant for a few days, or you may be given a prescription formula to use. If the pain is internal, treatment will be based on the cause.