Most cats genuinely never need a bath. Their tongues are designed to be effective cleaning tools, and daily self-grooming typically keeps even long-haired cats clean and presentable. But there are legitimate occasions when bathing is necessary — a cat who has gotten into something toxic on their fur, a cat with a severe skin condition requiring medicated baths, or a cat who is too obese or arthritic to groom themselves properly.
Before the Bath
Prepare everything before you bring the cat near water. You will need: cat-specific shampoo (never use human shampoo, especially not products with strong fragrances), a large towel or two, a sink or basin with a few inches of lukewarm water, cotton balls for ear protection, and treats for reward. A rubber mat in the sink or basin prevents the cat from slipping, which causes panic. Trim nails beforehand if possible.
The Bathing Process
Fill the sink with 3-4 inches of lukewarm water — test with your elbow, it should feel neutral. Protect the ears by placing cotton balls gently in the outer ear canal (not deep). Wet the cat's fur thoroughly with a detachable shower head or a cup, avoiding the head and face. Apply shampoo and work it into a lather gently, massaging the skin. Rinse thoroughly — all soap residue must be removed or it will cause skin irritation. Towel dry immediately and thoroughly.
Drying
Cats are sensitive to being towel-dried roughly. Use a gentle patting motion rather than vigorous rubbing. For long-haired cats, a blow dryer on the lowest heat setting can help, but many cats find the sound stressful. A warm, dry towel in a carrier with the door closed can be effective. Keep the cat in a warm room until fully dry — wet cats lose body heat rapidly.