Homeopathic medicines claim to improve one's immunity. If homeopathic medicines have any benefit it seems to be on the long term and not when symptoms have already manifested themselves. The same can be said for vitamins and mineral supplements. Traditional medicine still maintains that proper nutrition, adequate daily rest and minimizing negative stress in our lives, does more for the immune system than any so-called remedies. What you believe to be recurrent colds may actually be exacerbations of chronic sinonasal infections.
Allergies are a common underlying cause.
Allergies will cause swelling of the lining of the nose and sinuses and favour the development of infection. Anatomical deformities of the nose and sinuses such as deviations of the nasal septum, often lead to mechanical obstruction of the sinus openings and narrowing of the nasal passageways. The added swelling of the nasal lining by the cold virus simply favours the retention of secretions of the sinuses. Two to three common colds a year may be acceptable, particularly if you travel a lot. I caught a cold and I have a recital tomorrow.