Shampoos, soaps, sprays, lotions, creams, baths and the like build a group of miscellaneous products of variably quality and efficacy that have been used for decades to control fleas, ticks, mites, lice, mosquitoes and other external parasites of pets, long before the introduction of newer generation products such as spot-ons.
Most of them are ready-to-use; a few ones (e.g. baths) may need some previous preparation.
Such products are not used on livestock. Dressing for the control of fly maggots bear some similarity.
Parasiticidal products for bathing dogs and cats against external parasites are usually concentrates (liquid or solid) that have to be diluted in water. The pets are then treated in various ways: immersed, wet with a sponge, etc. Such products are sometimes identical with those used for spraying or dipping livestock, but packed in much smaller containers.
Besides the supposed insecticidal or tickicidal effect, many such products often claim other complementary cosmetic properties.
A common feature of such products in many countries is that they are not submitted to the same strict registration norms and requirements as "real" veterinary medicines (e.g. injectables, spot-ons, tablets, etc.). This means that their efficacy and safety have not been investigated as thoroughly as for approved veterinary medicines and pesticides.
They are sold mostly "over the counter" (OTC) in supermarkets, pet shops, online shops, etc. without a prescription, and often without any customer support or training. The use instructions of many such products are often not precise and open to different interpretations that make it easier to use them inadequately. The result of all these factors is that these products do not enjoy a good reputation as reliable parasiticides.
In fact, the use of such products in many countries has significantly declined after the introduction of much more potent and effective new generation parasiticides against fleas and ticks such as spot-ons.
If spot-ons are toughies, than shampoos, soaps, powders and the like are softies. The softies are also significantly cheaper.
Most of these products contain rather old generic active ingredients such as:
- Amidines (mostly amitraz): tickicides, acaricides, lousicides.
- Carbamates (e.g. carbaryl, propoxurr): broad spectrum insecticides, acaricides.
- Insect development inhibitors (e.g. methoprene, pyriproxyfen).
- Organophosphates (e.g. diazinon, chlorpyrifos) broad spectrum insecticides, tickicides, acaricides, lousicides.
- Synthetic pyrethroids (e.g. deltamethrin, permethrin) broad spectrum insecticides, tickicides, acaricides, lousicides.
Newer generic insecticides such as neonicotinoids (e.g. imidacloprid), phenylpyrazoles (e.g. fipronil) and spinosyns (e.g. spinosad) are slowly replacing the older active ingredients.
Numerous such products contain also natural insecticides and/or repellents such as pyrethrins, d-limonene, linalool, etc.
Some products contain a mixture of various active ingredients, often with a synergist to enhance the efficacy.
Depending on the active ingredient(s) they contain, these products offer some control of fleas, ticks, mites and/or lice. A few products offer some protection or repellent effect against flying insects such as mosquitoes, black flies (=gnats), midges, sandflies, etc.
All these products act by contact with the parasite. No product in this category contains parasiticides with a systemic mode of action, i.e. acting through the blood of the pet. None of these products controls internal parasites such as roundworms, tapeworms or flukes.
Efficacy against parasites
As a thumb rule, these type of "soft" products achieve a curative efficacy of 60%-90%. They are significantly less effective than insecticide-impregnated collars and spot-ons, and also less reliable. But they can be good enough for a quick fix to clean an infested pet.
The weakest point of these products is their rather short protection against re-infestation, i.e. their residual effect. A few such products may protect pets for a up to a week, but most products do it only for one or two days. A longer protection would require treating the pet every 2 to 3 days.
There are numerous reasons for a shorter protection, e.g, that they are quickly washed away (rain, splashing, etc.), or are broken down by sunlight, or evaporate quickly, etc. They can bring short-term relief, but are not adequate for controlling large flea populations or for protecting pets against re-infestation with ticks in highly infested areas (e.g. farms, rural areas).
Another reason for poor efficacy against fleas is that they may be already resistant to the active ingredients (see below).
Summarizing, don't expect miracles from insecticidal shampoos, soaps, powders, creams and other "soft" products.
Resistance of parasites to insecticides
Resistance of fleas to "veteran" insecticides of chemical classes such as organophosphates, carbamates and synthetic pyrethroids is frequent worldwide. The fact is that most shampoos, soaps, powders, sprays and the like contain such insecticides. For such products it is possible that they may not work as expected due to resistance.
However, most pet owners do not have the means to find out whether the fleas that plague their pet are resistant or not. Consequently, if a product doesn't work and there is no reason to believe that it is due to incorrect administration, the best is to try another product with an active ingredient of a different chemical classes, because different chemical classes have mostly diferent modes of action.
There are no yet reports on confirmed resistance o fleas to the newest active ingredients such as imidacloprid and fipronil.
There are a few reports on resistance of the dog tick (Rhipicephalus sanguineus) to organophosphates and synthetic pyrethroids. But this does not seem to be a widespread problem as it is for fleas.
Such products are usually safe for pet owners. However, it is better for children to avoid close contact with pets that have been treated with organophosphates, carbamates or synthetic pyrethroids, which can be toxic and/or irritant for the skin and the eyes.
Pets usually tolerate these products well, but be aware that some active ingredients can be safe for dogs, but toxic for cats, notably permethrin (and other synthetic pyrethroids) and amitraz. Consequently, never use on cats products that are approved only for dogs!