Yes, teeth whitening is safe when done properly, whether through professional treatments or over-the-counter products. However, overuse or improper application can cause issues like enamel damage or tooth sensitivity, so it's essential to follow instructions and consult your dentist for advice.

The effects of teeth whitening typically last anywhere from 6 months to 2 years, depending on factors like your diet, oral hygiene, and lifestyle choices (e.g., smoking or drinking staining beverages). Regular touch-ups may be needed to maintain the results.

Teeth whitening is most effective on extrinsic stains caused by food, drink, or smoking. It may be less effective on intrinsic stains, which are deeper and caused by factors like aging, certain medications, or trauma. In such cases, alternative treatments like veneers may be needed.

It depends on the method and your oral health. For in-office treatments, typically every 6 to 12 months is recommended, while at-home products should be used according to the manufacturer's instructions. Overuse of whitening products can cause damage to your enamel and lead to tooth sensitivity.