“How long does it take for allergic conjunctivitis to go away?”

It depends what he is allergic to. If you can figure it out. He can be cured, otherwise we have different drops to take care of his symptoms. If he has seasonal allergies they will recur every time that season comes around. You need to be prepared with his medicine before symptoms start. You will be ahead of the game

Until exposure to allergen is terminated.

Unfortunately, there is no standard time for all cases. A lot of it depends on if the allergen that is causing the allergic conjunctivitis is still present in the environment. For some kids/people, it can be a chronic condition that is quite difficult to treat. For others it can easily be controlled with drops and lifestyle changes. After starting treatment, the symptoms may not resolve all the way, but improve with time as the medicine works.

Red eyes should always be examined by a health professional, because there are lots of reasons for red eyes. If the eyes are red AND itchy, trying an over the counter allergy drop, artificial tears put in the fridge and cool compresses can be an easy first step to see if that helps. If it doesn’t, definitely seek additional support with an eye exam and alternative therapies.
Good luck to her!

Allergic conjunctivitis may linger or persist for a long time if the causes are still present in the environment.