I'll be totally honest when I say I only use flea meds if necessary. Like if I bring in a foster who has a particularly bad case of fleas that I didn't catch beforehand, I'll treat everyone. But in 7 years, and with 3 cats and 10+ cats at any given time, I've NEVER had a flea problem. And I've brought in some strays absolutely crawling with them with no other choice than to bring them in the house. And I never have had to do it in winter months, usually between Nov and March or April. Its just too cold in WV for fleas. But, I've been lucky I guess.