There is a common assumption that because you can buy sheath-cleaning products in a shop, this is a job to do yourself. I strongly advise against it, for the same reason you wouldn't do your horse's feet or teeth yourself. Many of the abnormalities horses develop here are very subtle. It takes real experience, a trained eye and a trained feel to know what is normal and what isn't. In my experience, at least one in ten horses I treat has some abnormality worth noting. It usually isn't sinister, but it's something to monitor, and if I find anything, I will always advise you to speak to your vet. Roughly one in eighty horses I treat shows a skin change that a vet later diagnoses as squamous cell carcinoma. This cancer is particularly common in geldings, because they don't self-clean. In the wild, nature manages all of this. Once a horse is domesticated and gelded, it doesn't happen, so we have to manage their hygiene for them. Because it's all tucked away and out of sight, it's easily neglected, and problems here can quietly sit behind behavioural issues and other health conditions. This is why the check matters more than the cosmetics, and why catching things early is the whole point.