Yellowing teeth are very common and usually not a sign of any health issues. For effective at-home whitening, look for products containing carbamide peroxide or hydrogen peroxide. For the safest and most noticeable results, I highly recommend visiting your dentist. They can provide professional in-office bleaching, custom-fit take-home whitening trays, or a professional dental cleaning (scaling and polishing) to remove stubborn surface stains. Please avoid highly abrasive charcoal or DIY remedies, as they can permanently wear down your protective tooth enamel.