Chicago police and fire responded to the scene around 8 a.m. After an hours-long investigation, authorities told ABC News the substance was identified as baby powder and there was no threat to the public.
Buses were made available to shuttle train commuters between the Sheridan, Addison and Belmont stations during the investigation.
CTA officials recommended the No. 22 Clark, No. 36 Broadway, No. 8 Halsted, No. 147 Outer Drive Express or No. 151 Sheridan buses as alternates.
Normal Red Line service was restored around 11 a.m.