I've used Crest teeth whitening strips a fair few times over the past few years, anyone who lives within the UK will know just how hard it is to whiten your teeth on a budget and these are the only product I've found to actually work without breaking the bank. That being said, there are a couple of downsides which I'm now going to talk you through. Most of you will probably know that Crest whitening strips aren't available to buy in the UK, thus meaning you need to find an online seller that has imported them from the US. I did a little research and found out that the reason for this is that they are banned for sale by the British Dental Association as teeth whitening products containing over 0.1% hydrogen peroxide (bleach) are not allowed for sale, Crest whitening strips contain between 6-14%. The issue here is that bleach can break down the enamel on the teeth which causes sensitivity and if used irresponsible can result in irreversible damage. In essence this means if you were to use the whitening strips daily or go through a course more than a few times a year then you'd be causing your teeth more harm than good.
In my experience I've found that around the halfway point of a 14 day course that I can sometimes get a sharp shooting pain in the nerves of my teeth that lasts only just a few seconds but can still sometimes be a cause for concern. I always find the results of how whitened my teeth become outweigh the slight risk factor and as I would only ever use the 14 day course twice a year at most I don't see any real harm ever being done. The point I'm trying to make here is that regardless of if they have good reason to be banned or not in the UK, it's worth knowing the reason as to why and then you can make an informed decision about putting concentrated levels of bleach onto your teeth. If you decide to go ahead and buy a set of whitestrips, the main issue is finding a seller that sells the real deal and not just some fake knock offs. I'd also say don't bother with the cheaper and less effective strips that claim to be more gentle, they really do end up just doing next to nothing.
My preferred version are the 3D Professional Effects Advanced Seal Whitestrips, these mould around teeth perfectly and stay put for the hour or so that they need to be left on for. A big tip of mine is to try and get your teeth as dry as possible before applying them as this way they won't slip and slide around. I go for the 14 day course as I find that it leaves my teeth looking as white as I'd want them without damaging them in any way, but if you're teeth are needing a complete overhaul then look at going for the full 20 day treatment. I buy mine from this eBay seller and have found them to be what I believe is authentic, but if you're at all concerned then go for the sealed box option. I'd highly recommend using Crest Whitestrips, I'm always so impressed by the results and think they are worth every penny to completely whiten my teeth twice a year.