The kidneys and urinary tract are responsible for getting rid of waste products from the body. Essentially the kidney acts as a course filter for blood; it then performs a secondary scavenging act to pick up those substances which have slipped through the filter that should not. This is a highly energy requiring process and one can measure this glomerular filtration rate with a blood test. This gives us a useful early warning mechanism for kidney damage.
Kidneys can be kept in the best possible health by observing all the interventions in Category:Your very good health!.
Any kidney symptom such as loin, loin to groin pain, recurrent cystitis should always be taken seriously and fully investigated. The bare minimum of investigation is urine analysis, routine blood tests, including GFR and ultrasound of the kidneys. Together with blood pressure measurements.
If all the above investigations are normal, but one continues to have symptoms then the likeliest explanation is going to be allergy.