While clean and hygienic conditions do prevent rapid growth of cockroaches in the house, cockroaches may still enter through drain pipes or hitch hike into your house along with groceries, crates, gas cylinders etc.
It depends upon the kind of pest control treatment being given. All pesticides are harmful. But chemicals used at home by reputed Pest Control Professional are tested and proven for home use. These are chemicals developed for in-home application as against agricultural pesticides designed for field application which are more toxic. Secondly, targeted delivery at the right place and the correct dose makes all the difference. Reputed Pest Control Professional take precaution to ensure the safety of humans and domestic pets.
The household insecticides available in the market are short term solutions which only kill the pests you see but spare those which are hidden. Professional pest control involves identification of the type of the pest, its harbourages, elimination at its source - delivering long lasting solutions.