Kwell should be used with caution neurotoxic reactions, carcinogenicity in lab animals and blood disorders have been reported as a result of the normal use of lindane shampoos. Effectiveness Parents sometimes report that these products are not effective and often blame resistant lice or the product. However, sometimes the problem is that parents are not using these products according to label directions. The treatment is not repeated 7-10 days later, as directed on the label. Because the head lice nit stage is resistant to chemicals, the treatment must be repeated to kill lice that hatched after the first treatment.
Less product is used than is recommended on the label.
Because these products are expensive, parents understandably want to save shampoo to treat another child or for a later treatment. It is important to use the entire amount recommended on the label. Any less can reduce the effectiveness of the shampoo. These products cannot be used like regular shampoos. Read and follow all label directions.