Mast Cells

• All people have mast cells in their bladders. For reasons not known to scientists, people with IC tend to have a higher number of such cells, leading them to be more susceptible to inflammation.
  
  

Allergies

• Many people with IC suffer worsening of symptoms or flares of bladder pain and urinary frequency during times when people typically suffer from seasonal allergies, such as spring.
  
  

Prescription Antihistamine

• Doctors often prescribe hydroxyzine, which has anti-anxiety properties and a mild sedative effect as well as the ability to degranulate or shrink mast cells, reducing symptoms.
  
  

OTC Antihistamines

• Some over-the-counter antihistamines work to reduce symptoms as well, such as loratadine and diphenhydramine. OTC allergy medication containing decongestants tend to aggravate bladder symptoms.
  
  

Histamine Blockers

• OTC histamine blockers, such as cimetidine and ranitidine, work to reduce acid in people who suffer from acid-reflux and provide beneficial effects for some people suffering from IC.