Flea collars are unnatural. Mosquitoes and flies are natural, though most people find them to be a nuisance and prefer the unnatural comfort of mosquitoeless nights and flyless barbecues. Eating meat might be a natural act, but eating cooked meat is unnatural. Most sauces put on meat are made with both natural and artificial ingredients. Salt is natural, but some healthy people avoid salt like the plague.
Civilization is unnatural.
Indoor plumbing is unnatural. Corrective lenses are unnatural. So are automobiles. To have a broken arm set by a physician is unnatural. To let it heal spontaneously would be natural, even if debilitating for life.