 [ Symptoms ] i have been diagnosed with a chairi malformation experiencing a lot of widespread pain is it autoimmune disease [ Disease ] it is not so much a question of how long it takes fish oil to get out of your body but more how long it will take to get the reaction to go away that depends on how sensitive you are if you are not allergic put some benadryl gel on the rash or take a benadryl tablet diphenhydramine to help reduce the reaction if you start having trouble breathing or get other symptoms of anaphylaxis see a doctor or the er immediately