For Chihuahuas, the harness-versus-collar debate has a clear winner: harnesses are strongly recommended over traditional collars for leash attachment. Chihuahuas are highly susceptible to tracheal collapse, a condition where the cartilage rings supporting the windpipe weaken and flatten, and any pressure on the throat from a collar during pulling or sudden stops can contribute to or worsen this condition. A well-fitted harness distributes force across the chest and shoulders, eliminating throat pressure entirely.
The best harness styles for Chihuahuas are step-in designs or vest-style harnesses that wrap around the torso. These are easier to put on a small, wriggly dog than over-the-head designs, and they provide broad surface contact that minimizes pressure points. The harness should fit snugly enough that the dog cannot back out of it, a common escape tactic for Chihuahuas, but loose enough that two fingers can slide comfortably between the harness and the dog's body at any point.
Collars still serve an important purpose as a carrier for identification tags and registration, even when a harness is used for walking. Lightweight, flat collars in extra-small sizes are appropriate for this purpose. Avoid heavy hardware, chain links, or prong-style collars, which are entirely inappropriate for a toy breed. Breakaway collars, which release under pressure if the collar catches on something, add a safety layer for dogs that wear collars indoors.
Leashes for Chihuahuas should be lightweight and proportional to the dog's size. A heavy leather leash designed for a German Shepherd adds unnecessary weight and bulk for a five-pound dog. Thin nylon or fabric leashes in four- to six-foot lengths provide adequate control without dragging the dog down. Retractable leashes are generally discouraged for Chihuahuas because the thin cord can cause injuries and the variable length makes it difficult to maintain close control near traffic, larger dogs, or other hazards.