What would happen if i used the lice shampoo more than the recommended once a week?

Toxicity: Lice treatments are basically insecticides and if over-used will cause not only skin irritation but can cause neurologic toxicity (damage to the central nervous system). Children are especially susceptible to this.

Waste of product: There are some products with potential toxicity if used too often but the strength of these products makes it unlikely. I sometimes recommend retreating a week or so later to pick up any leftover bugs. It takes 10 days for the new louse to begin reproducing.