WordWeb Online

1. Not sanitary or healthful
   "unhealthful open sewers"
   - unsanitary, insanitary
    
2. Detrimental to good health
   "unhealthful air pollution"; "unhealthful conditions in old apartments with peeling lead-based paint"
    
3. Detrimental to health
   - insalubrious, unhealthy

See also: crippling, cytopathogenic, disabling, incapacitating, infected, infective, morbific, nonmedicinal, pathogenetic, pathogenic, septic, toxic, unhealthfulness, unhealthy, unhygienic, unmedical, unmedicative, unmedicinal, unwholesome

Antonym: healthful