One of the treatments for fungal nail infections is amorolfine nail lacquer. It’s medicated, but as far as I know it’s not a pretty colour. There’s also a bit in the instructions about not using nail varnish while you’re using amorolfine. The question I got asked (by a man) was, why should this be so?
If he’d been a woman, he’d probably have known the answer. Not because men are inherently stupid, or because women are inherently good at organic chemistry, but because more women wear nail varnish than men. I hardly ever wear it myself, but I still have a couple of bottles which are lasting quite well, considering I don’t remember when I bought them.
But the thing that you know, if you’ve used nail varnish more than once or twice, is that a new layer of nail varnish can dissolve an older layer. It’s useful if you’re caught short without any nail varnish remover, but not so good if you’re trying to repair chips or make really great designs.
The reason it works is because of the solvent: most nail varnishes use ethyl or butyl acetate as the solvent. This evaporates when the nail varnish dries, leaving a hard layer. If, however, you add more solvent (as in, more nail varnish), then the original layer will be dissolved again and you can wipe it off.
And when it comes to amorolfine, it’s just nail varnish with an antifungal in it instead of pretty colours – and it uses the same solvents as ordinary nail varnish. So if you put ordinary nail varnish on over the top of your medicated antifungal nail varnish, you risk your antifungal nail lacquer either coming off or getting diluted. And if that happens, there’s the risk that it won’t work as well. So, it’s safer all round just to have boring nails until the infection is gone.