How long can you wear contact lens without hurting your eyes?

What kind of lens? Although there are extended wear contact lenses, i recommended daily removal before sleeping. Tears provide anti-infective compounds and enzymes which are in short supply during sleep when tear production drops. This puts the eye at greater risk for potentially sight threatening infections.
It depends on lens. The safest way to wear lenses are the type which are replaced or sterilized every day. With any type of extended-wear lens, the risks of infection, corneal irritation, allergy or blood vessel growth increase. We recommend our patients to stick to the daily wear or replacement regimen with daily disinfection.