Hi rjohn, Good day! The answer depends on when the shampoo is used in relation to the Frontline application and the type of shampoo. Here’s a breakdown: 📌 If used immediately before applying Frontline: It's actually recommended to bathe your pet, if needed, at least 24–48 hours before applying Frontline. This ensures the skin’s natural oils are replenished, since these oils help distribute the Frontline across the skin and coat. 📌 If used soon after applying Frontline: Bathing your pet within 48 hours after applying Frontline can reduce its effectiveness. Frontline needs about 24–48 hours to fully absorb into the sebaceous (oil) glands of the skin, which act as reservoirs for slow release over time. 📌 Once Frontline has fully dried and settled (after 48 hours): Most regular pet shampoos (non-medicated, non-degreasing) won't wash Frontline off. Frontline is designed to be waterproof after 48 hours, so gentle bathing after this window typically won’t interfere with its effectiveness. 🚫 Exceptions: Medicated shampoos (especially those that are anti-seborrheic, anti-fungal, or contain strong detergents) or degreasing shampoos might strip skin oils and potentially reduce Frontline’s staying power. Frequent bathing (even after 48 hours) or swimming several times a week can cumulatively lower its residual effectiveness. ✅ Bottom line: Wait 48 hours after applying Frontline before bathing your pet. Use mild, non-medicated pet shampoos to avoid reducing its effectiveness. Avoid frequent or aggressive baths if possible while using a topical flea and tick treatment. Thanks