Unplug the Holmes air purifier from the electrical outlet. Place the unit on a table.
Remove the front grill from inside the air purifier. Grasp the indentation on the right side of the purifier's front housing, and pull open carefully. Grab the top area of the grill and slowly pull it up and out of the purifier.
Fill a sink with warm water and 2 tsp. of mild liquid dish soap. Place the grill into the soapy water. Gently wipe the grill with an old rag, removing dust and dirt. Rinse the grill in warm water and dry with a dish towel.
Wipe the housing of the Holmes air purifier with a soft, clean cloth. Use an old toothbrush to dislodge dirt in the air vents. Wipe the inside of the purifier with the cloth. After drying the grill completely, place it back inside the purifier. Close the door to the purifier and make sure it snaps shut.