...i just started wondering what is bad about those repellants? What's the risk? I'm still not planning on using them, i just want to have an educated reason to justify to myself why we're not! Thanks!
They're not 'repellents'. They're killers. That is, toxic chemicals that kill the fleas/ticks - insecticide, in other words. When we apply those chemicals to our pets, we're slathering them in insecticide - most of which kill insects by interfering with the nerve cell transmissions from the brain, resulting in paralysis then death. In most cases, the dose is low enough that we don't notice ill-effects on the dog, but the fleas are killed. It is only "sensitive" individuals who have obvious ill effects.
That is one of the reasons why ALL of those products carry warnings that they are not to be used on animals who're already unwell, and specific veterinary advice should be sought before using them on pups, seniors, pregnant or lactating animals.
But you know, things are usually quite extreme by the time we notice physical effects in others. The dog can't tell you about his tummy ache, or his migraine. It's only if it's severe enough to have him obviously unwell that we are aware there is any effect at all.
Some of the listed side effects include lack of appetite, vomiting, diarrhea, lethargy, itching, difficulty breathing, or reddened skin. Fortunately, reactions that severe aren't common. But as above - the dog can't tell you about lesser symptoms. And he may be getting this treatment regularly.
Then there are the oral types that either kill the fleas, or like Program that inhibit insect development (so in effect, it kills the larvae). These are generally safer, because they're attacking a growth process unique to insects. But the dog still had to consume that.
So that's basically what you need to think about with flea/tick treatments. And that's NOT to say don't use them. Flea infestations and ticks have their own health effects. But we all have the
responsibility to understand what we're putting on our pets, and the effects it may have - especially if we're doing it monthly for an extended period. No toxic chemical is without some effects, even in relatively small doses - and effects can build up over time too.
So you just need to weigh up the relative risk and benefits. Do you happen to live somewhere where fleas and ticks are a significant problem? Where nasty diseases spread by those insects are rife? If you do, then regular flea and tick treatment is probably the lesser of the two evils.
If things aren't that extreme where you are - then you might consider natural deterrents (like garlic) and treating any actual infestations on an "as needed" basis. Or treating only during the worst risk months.
But what none of us should do is just mindlessly pump our dogs full of insecticide for fleas, and pesticide for possible parasites, without a thought to the actual need for it or the long term effects it can have on the dog. And some people do! There hasn't been a flea seen in years in their area, yet the dog is still treated. It's never had worms - but they de-worm every three months like clockwork. IMO, it's better all round to just maintain an awareness of the possible effects of chemicals on your dog - and simultaneously, an awareness of the risks for where you live. Then make decisions on what treatments to use (if any) according to those conditions. And if you're lucky enough not to have to use any (or many) treatments at all - that's good news for all concerned (dog included).
A couple of short veterinary articles on various flea/tick treatments, and on the active ingredients:
http://www.peteducation.com/article.cfm?cls=2&cat=1588&articleid=2627
http://www.peteducation.com/article.cfm?cls=2&cat=1588&articleid=598