How to Brush the Trouble Zones: Armpits, Behind the Ears, and the Groin

Armpits, behind the ears, the groin, and under the collar mat first because that's where the coat moves the most and stays damp the longest. Work each zone with your fingers before any tool touches it, then comb from the outer edge of the tangle inward while you hold the hair at the base so a pull stops at your hand instead of reaching the skin. If a mat won't let go of the skin, or the skin under it is red, moist, or smells off, that stops being a brush job and becomes a groomer's or a vet's.

Why these spots go first

Everywhere else, hair mostly just sits there. Here it's under constant motion — a leg swinging with every step, a jaw working — plus the moisture that collects in a tight skin fold, so loose hair that would blow apart on the ribcage felts together instead. A collar or harness strap adds a third ingredient: rubbing the same patch of fur on every walk.

PDSA's grooming guidance flags this same pattern (the line is written for cats, but the same folds apply to a dog), calling the armpits, legs, tummy, and tail "danger zones for matting." Those are the spots owners skip because they're awkward to reach, while the back and top of the head, which barely mat at all, get most of the brushing. The Royal Kennel Club makes the same point from the other side: medium- and long-coated breeds need grooming "on a much more regular basis" specifically to keep the coat "tangle and matt-free."

The order that keeps the pull off the skin

Fingers first, always. Work the hair apart with your fingertips before any comb goes near a tight zone — a loose tangle separates with a little pressure; a real mat doesn't move.

For a mat, the American Kennel Club's advice is to "start from the outer edge of the mat and work your way toward your dog's body" rather than attacking the middle. Peel a few strands loose at the tip, then move closer to the skin and repeat, with your free hand holding the hair flat at its base — that's what keeps a tug landing on your fingers instead of the follicle.

A fine comb earns its place here because it tells you the truth about a tight zone. Our 2-in-1 pet grooming comb set includes a dual-sided detangling comb (7.5 inches (19 cm) long, with a fine 36-tooth section and a wider 26-tooth section) plus five fine combs with rounded, polished tips. Run the fine side through a loosened section: glide all the way to the skin and the zone is done; stop partway and you've found where the mat is still tight.

A small tangle, not a full mat

Behind the ear or in the groin fold, a snag is often small enough that a full detangling session is overkill. The rotating side of our 2-in-1 undercoat rake and 360° detangling comb is built for that — the teeth pivot to follow the coat's direction and flex up and down, so a small snag sends some force into the tool rotating instead of straight into your dog.

The rake side of that same tool doesn't belong in these zones. It's built to pull loose undercoat off flatter, thicker-coated areas, and armpit or groin skin is thin, close to the surface, and folded — there's little coat to cushion rake teeth there. Save it for the back, sides, and haunches.

Position the dog, not just the tool

Have your dog lie on their side for armpit and groin work — it opens the fold and takes their weight off the area you're brushing. Do one zone per session, not all four, and stop while your dog is still comfortable rather than pushing to "finish." We've written more on keeping sessions short enough that a dog never wants to leave, which applies directly here, since these zones are usually why a dog started disliking brushing in the first place.

When it stops being your job

Put the comb down and call a groomer or a vet if the mat is tight against the skin and won't shift with the outer-edge technique, you can't get even the fine comb underneath it after a few short sessions, or the skin under it is red, moist, or has a smell. That last one is a vet matter outright, not something to keep brushing at.

Don't reach for scissors near any of it. A mat tight to the skin pulls the skin up into itself, so it sits closer to a blade than it looks, and you'd be cutting toward something you can't see — truer in the armpits and groin than almost anywhere else on the dog. We've laid out the fuller split of home versus professional tasks in this breakdown.

If your dog has a short, smooth coat

None of this is really for you. A Lab, a Beagle, a pug: coats without an undercoat or much length don't build the tangle that felts into a mat, even in these folds, because there isn't enough loose hair collecting to catch on itself. Skip the comb work: check the skin in those folds while petting your dog, and move on. This routine is for medium, long, curly, and feathered coats — doodles, retrievers, spaniels — where friction and moisture have hair to work with.

Frequently Asked Questions

Q: How do I tell a tangle from a real mat?

A: Work it with your fingers first. A tangle loosens with light pressure; a mat holds its shape as one dense patch that doesn't give. If your fingers can't tell, try the fine comb — if it stops and won't slide through, treat it as a mat.

Q: My dog won't hold still for the armpit or groin at all. What then?

A: Shorten the session further rather than pushing through. A few seconds of calm handling with no comb, ending before any resistance, does more for next time than a longer session that ends in a struggle.

Q: Is matting under the collar a coat problem or a fit problem?

A: Often both, but check the fit first. A strap that slides loosely or grinds against the same patch on every walk will mat that spot no matter how often you brush it. Reposition or pad the strap, then keep brushing the area as usual.

Sources

• PDSA — How often should you groom your pet? (https://www.pdsa.org.uk/pet-help-and-advice/looking-after-your-pet/all-pets/grooming-pets)
• American Kennel Club — How to Overcome the 4 Biggest Dog Grooming Challenges (https://www.akc.org/expert-advice/health/how-to-overcome-the-4-biggest-dog-grooming-challenges/)
• The Royal Kennel Club — How to groom my dog? (https://www.royalkennelclub.com/health-and-dog-care/health-dog-care/health/health-and-care/a-z-of-health-and-care-issues/dog-grooming/)

Shop the tools: Brushes & Deshedding Tools. Fine combs and rotating detanglers built for tight, tricky trouble zones.