Background: Many asthmatic patients allergic to dogs refuse to part with their dog, and it is essential to develop techniques for lowering exposure with a dog in the home. Objective: This study investigated the effect of dog washing on the subsequent recovery of Can f 1 from dog hair clippings and on the airborne allergen over a 7-day period. Methods: Dogs, which had not been washed for at least the previous 3 weeks, were washed with a hand-held shower and proprietary shampoo. Hair clippings and dander samples from 25 dogs were collected before and immediately after washing. After these initial studies, 16 dogs had a small tuft of hair clipped from the collar or spinal area before washing and then daily for the next 7 days. Air sampling was performed in 5 homes, and the air samples were collected (airflow rate, 9 L/min) over an 8-hour period per day on 10 consecutive days (3 days of baseline sampling before washing and then 7 consecutive days after washing). Can f 1 level was measured by using 2-site ELISA. Results: Washing significantly reduced recoverable Can f 1 from clippings (84% reduction: from 73 μg/g to 12 μg/g [geometric mean]; P <.0001) and from dander samples (86% reduction: from 347 μg/g to 50 μg/g [geometric mean]; P <.0001). There was a significant reduction in Can f 1 levels in dog hair over the observed 8-day period (F = 18.4, P <.0001). By using a multiple comparison test, this observed significance was found to be due to the difference between the baseline levels and those on days 1 and 2 after washing, with no difference in the baseline Can f 1 compared with days 3 to 7. Airborne Can f 1 levels showed a downward trend, which reached statistical significance when the data were grouped into 3 sampling periods as follows: baseline (ie, mean of 3 days before sampling) was compared with days 1 to 4 after washing (41% reduction, 95% CI 13%-60%) and days 5 to 7 after washing (61% reduction, 95% CI 2%-84%; P = .014). Conclusions: Washing the dog reduces recoverable allergen from dog hair and dander. The dog needs to be washed at least twice a week to maintain the reduction in recoverable Can f 1 from its hair. Washing the dog achieves a modest reduction in the level of airborne Can f 1 in homes with a dog.