What Frontline is
Frontline is a brand of topical (spot-on) flea and tick treatment. It comes as a small liquid pipette that you apply to your dog’s skin, and different versions exist for different needs and species. This article describes the general way spot-ons such as Frontline Plus are described by the manufacturer. Always read the label of the exact product you have, because ingredients, ages, weights and directions differ.
How it spreads over the body
You apply the liquid to a single spot on the skin, usually between the shoulder blades, where your dog cannot lick it off. According to the manufacturer, the active ingredients then spread across the skin surface and coat, helped along by the natural oils in the skin. The product mostly stays in the skin and coat oils. Over the following days the ingredients are described as continuing to distribute across the body.
For this to work, the product needs to reach the skin. Part the fur so the liquid touches skin instead of sitting on top of the coat.
How it kills fleas and ticks
Frontline Plus is described as containing two active ingredients:
- Fipronil, which acts on the nervous system of fleas and ticks.
- (S)-methoprene, an insect growth regulator that is described as interfering with the development of flea eggs and larvae.
The key idea is that parasites are affected when they come into contact with the treated coat and skin, so they generally do not have to bite first. Even so, some insects may still be seen for a short period before they die.
How to apply it properly
- Check the label for your dog’s weight range and age. Choose a dog-specific product.
- Part the fur at the application site so you can see skin.
- Squeeze out the contents onto the skin, not onto the surface of the coat.
- Keep other pets and children from touching or licking the area until it has dried.
- Follow the label instructions about bathing and swimming around the time of application.
- Wash your hands afterwards.
Never use a product made for dogs on cats unless the label explicitly says it is suitable. Some dog products can be dangerous for cats. Many dog flea products contain permethrin, which can be fatal to cats. A cat can be exposed by grooming or sleeping with a recently treated dog. If a cat is exposed, call your vet or a poison helpline straight away: ASPCA Animal Poison Control Center, (888) 426-4435, or Pet Poison Helpline, (855) 764-7661. Both are open 24 hours a day and may charge a fee.
How to tell if it is working
Signs the product is doing its job include fewer fleas on your dog, less scratching and fewer flea droppings (small dark specks) in the coat over the following weeks. A flea comb is a simple way to check.
Two things can confuse owners:
- Fleas may still appear for a while. Most of a flea problem is typically in the home, as eggs, larvae and pupae. New adult fleas can emerge and jump onto a treated dog, where the product is meant to kill them. Treating the home environment can help, and our guide to alternative flea treatments covers practical household steps.
- Fleas may seem more active at first. Some owners notice fleas moving to the top of the coat before dying. This is not necessarily a sign of failure, but if you are still seeing live fleas after a couple of weeks, talk to your vet.
If fleas persist despite correct, regular use, the problem could be missed doses, heavy household contamination, poor application or reduced effectiveness in your area. Your vet can help work out which and may suggest another approach.
What it does not do
A flea and tick spot-on does not protect against heartworm or most intestinal worms. For the wider picture, read our flea, tick and heartworm prevention guide. Worms are discussed in do dogs need worming.
Safety notes
- Use only the product designed for your dog’s size and age.
- Watch your dog after application. Mild skin irritation at the application site can happen. Contact your vet if you see redness, persistent scratching, drooling, vomiting, tremors or lethargy.
- Tell your vet about other medications or health conditions, including past seizures, before starting any parasite product.
- Do not combine several flea products without checking with your vet.
When to see a vet
See your vet if the product seems not to be working, if your dog has a bad reaction, if your dog is a young puppy, elderly, pregnant or unwell, or if your dog has skin disease or an allergy to flea bites. For a severe reaction, seek urgent care.