Red itchy eyes - could this be caused by allergies?

My Weimaraner has very red, slightly irritated eyes and appears to be itchy at times. Could this be allergies? And can I give her Benadryl?

Red inflamed eyes should always be examinbed by a vet as this can be caused by infection, damage to the eye (ulcers), eyelid deformities, eyeball pain or skin disease. Allergies can cause red eye and antihistamines like benadryl can be used but only once other causes are ruled out. These other causes are potentially serious so you should get your dog examined particularly if they may be painful.

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