Westies are prone to allergies and dry skin issues, and bathing too frequently may aggravate these problems. Washing once a month or on a longer interval will generally not cause issues. However, frequent brushings are needed to keep the coat clean and oils evenly distributed throughout the coat.
Washing with a detergent-free, baby-oriented, or another soft skin shampoo will help keep a Westie's skin hydrated. Weekly washing of the inside of the ears with cotton balls will prevent oil and wax build-up and ear infections.