The answer to 'bathroom filthy' is that there are several common causes for a bathroom becoming excessively dirty or unsanitary. This can include a buildup of soap scum, mold and mildew growth, hard water stains, and general neglect of regular cleaning. Symptoms may include grimy surfaces, foul odors, and an overall unpleasant appearance.
In many cases, a thorough DIY cleaning using the right products and techniques can restore the bathroom to a clean and fresh state. This may involve scrubbing surfaces, using disinfectants, and addressing any underlying issues like poor ventilation. However, for more severe or persistent problems, it's often best to call in a professional cleaning service to properly deep clean and sanitize the space.