Many tick control products also affect other external parasites and some, most notably those containing the macrocyclic lactone compounds, also affect internal parasites. Use of these chemicals for tick control can also select for resistance in the other parasites. It is important to read the label to determine which parasites will be controlled. Resistance is a significant issue in ticks, buffalo flies and cattle worms and when choosing a chemical for tick control consider the possible effects of increasing selection for resistance in non-targeted parasites.