Is it likely the type of allergy causing allergic shiners could be a food allergy or a sinus or hayfever problem? My son has all year round?

Allergic Shiners. Generally indicate sinus or a hay fever problem. Try to insure good sinus drainage with gentle saline and consider Singulair (montelukast) or an intranasal steroid. All the best.
See MD. Hard to say with info offered--allergic shiners are caused by sluggish circulation associated with venous blood vessel congestion--therefore darker color. See your doctor to check.