Cello Handbook/The Bow
The tip of a wood bow is fairly fragile, so it is advised not to place it under undue stress (from tapping, dropping, etc.).
A typical cello bow is tightened by a cylindrical screw located at the frog end of the bow. While it is important to maintain tension during playing, leaving the bow tightened when not in use for extended periods of time may warp the shape of the wood and reduce its ease of use and quality of sound. Some players recommend leaving the hair loose but not entirely slack, so as to keep the hair straight.
The hair can be cleaned of excess oil or grease using shampoo or alcohol, although alcohol may damage the bow stick so care must be taken if using this method. If using shampoo, it is also important to ensure that the bow hair is entirely rinsed clean before playing or it may affect the sound quality.
Repairs to bows typically require a great deal of skill, and as a result it is recommended to take yours to a luthier or professional if necessary. For students and others who use inexpensive bows, often the cost of replacing the bow is less than that of repairing it.