Yellow teeth, despite regular brushing, can be due to several common reasons, such as natural tooth colour, surface stains from tea, coffee, or smoking, plaque or tartar buildup, or thinning of enamel over time, rather than poor hygiene alone. Improving appearance involves proper brushing technique (using a soft brush and fluoride toothpaste), regular flossing, and professional dental cleaning to remove tartar; if needed, a dentist may suggest safe whitening treatments for better results. Limiting stain-causing foods and drinks, rinsing the mouth after consuming them, and avoiding tobacco can also help maintain whiter teeth. If discolouration is severe or uneven, a dental check-up is important to rule out underlying issues and choose the most suitable treatment.