Laser irradiation at fluences below the damage threshold level of antireflection‐coated BK7 (grade A borosilicate crown glass) samples temporarily increases the measured laser‐induced damage threshold by about 40%. Because the surface damage threshold is sensitive to the irradiation history, it is necessary to control the test procedure to ensure reproducible and accurate measurements. Preliminary results indicate that adsorption of water is a principal factor involved in the deactivation of the conditioning enhanced laser damage thresholds.