Flea allergy dermatitis in dogs and cats
Introduction
Flea allergy dermatitis, or FAD, is an itchy skin condition caused by an allergic reaction to flea saliva. Pets with FAD do not need lots of fleas to be miserable. One or two bites can trigger days of itch. The goal is to stop the bites, calm the skin, and keep the cycle from starting again.
What it looks like
Dogs often chew around the tail base, rump, belly, and inner thighs. The skin may be red with scabs, and hair breaks from licking. Cats tend to overgroom and leave short, spiky “barbered” hair. You might see tiny crusty bumps on the neck or back, and the coat looks dull. Many owners never see a flea. That is common with FAD.
Why a small number of fleas cause big itch
With FAD, the immune system reacts strongly to proteins in flea saliva. A single bite can set off a widespread flare. That is why good control focuses on prevention and consistency, not just killing what you can see today.
The quick relief plan
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Treat every pet in the home with an effective flea product that suits their species, age, and weight.
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Dose on time and keep going for at least three months to clear the home environment.
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Clean the home. Vacuum carpets, rugs, sofas, and car seats. Empty the vacuum outside. Hot wash pet bedding.
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See your vet if the skin is broken or very sore. Many FAD pets need short-term anti-itch or antibiotics to settle the flare.
Ongoing prevention
FAD is usually a year-round management issue. Choose a product format you can give on time every time. Set reminders. If you switch products, make a clean change when the old one is due so you avoid gaps.
Bathing and skin care
Baths can soothe skin but will not replace flea control. Use a gentle, vet-recommended shampoo and follow label advice if you use a spot-on. Many pets improve with a short course of medicated shampoo while the skin heals.
Safety and label checks
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Dog products for dogs only. Never apply a dog product to a cat.
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Some dog spot-ons contain permethrin. Keep cats away from recently treated dogs as labels advise.
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Pick the right weight band and check minimum age.
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Do not stack flea products unless your vet tells you to.
Products we trust
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Dogs: Simparica Trio Chewable Tablet for Dogs — monthly chew with broad parasite cover. Match the weight band and follow the label.
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Dogs: Bravecto Chew for Dogs — long-lasting chew. Handy if you prefer fewer doses.
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Cats: Revolution Plus Spot-On for Cats — monthly, broad cover when used as directed.
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Cats: Bravecto Spot-On for Cats — long-lasting flea control. Check protection period and weight band.
FAQ
Do I need to treat even if I cannot find a single flea?
Yes. FAD pets often react to very low numbers. Keep up regular treatment and home cleaning to stop bites.
How long until my pet is comfortable again?
Itch often improves within two to three weeks once bites stop. Skin infections and hot spots take longer. Your vet can help with relief while the skin heals.
Can I just treat the itchy pet?
No. Treat every dog and cat in the home. Untreated pets can keep the cycle going.
Is bathing enough on its own?
No. Baths help comfort but do not prevent new bites. Use a registered flea product and keep to the schedule.
Not sure if it is FAD or something else?
Share your pet’s age, weight, photos, and symptoms and we will help you choose next steps — contact us.
Shop trusted flea, tick and worm protection for dogs and cats. Our vet-led team, headed by Dr. Feargus McConnell, BVSc, can help you build a simple plan that works for your household.
