Coat and Skin: The Science Behind Every Groom

Every decision on the grooming table, from which brush to pick up to whether a coat can be clipped short, depends on understanding how hair grows and how skin behaves. This lesson covers that science in plain terms: the hair growth cycle, the main coat types and what each needs, and why dog skin demands a gentler touch than most people expect.

You do not need to become a dermatologist. You need enough understanding to predict how a coat will behave, and to explain your choices to an owner.

How hair grows

Each hair grows from a follicle in the skin, and each follicle works in a cycle. There is a growth phase, when the hair lengthens; a short transition phase, when growth stops; and a resting phase, after which the old hair is shed and a new one starts to grow. Follicles do not all cycle at once, which is why most dogs shed a little all the time rather than going bald in patches.

What differs between coats is mostly the length of the growth phase and what happens to the shed hair.

• In many short and double coats the growth phase is fairly short, so hair reaches a set length and stops. Shed hair falls out, onto the floor and the sofa.
• In curly and continuously growing coats (the Poodle type, and many Poodle crosses) the growth phase is long, so hair keeps lengthening and needs regular cutting. When these hairs are shed, they tend to stay caught in the surrounding curls instead of falling away.

That second point explains much of a groomer's workload. Shed hair trapped in a curly coat tangles with the growing hair around it, and without regular brushing right down to the skin those tangles tighten into mats. It is also why owners are often told these dogs "do not shed": the hair is shed, it just stays in the coat until someone brushes it out.

Coats also change with age, season and health, so the coat you see on a puppy is not always the coat you will be grooming a year later. Seasonal changes in daylight and temperature trigger heavier shedding in many double-coated dogs, which is why they can seem to lose a whole layer of undercoat in a few weeks.

The main coat types

Groomers group coats by how they grow and what they need. Most dogs fit one type or sit between two.

Two practical points follow from the table.

Double coats are not usually clipped short. The coat works as a system: the undercoat insulates and the guard hairs protect the skin, including from sun. After close clipping, some double coats grow back unevenly or very slowly. Most groomers keep double coats in good condition by removing dead undercoat and only clip them short when there is a clear reason, such as severe matting or a vet's request. Lesson 3 works through exactly this conversation.

Wire coats change with clipping. Hand stripping removes dead hair from the follicle and keeps the harsh texture and strong color. Clipping cuts the hair instead, and over time the coat tends to become softer. Neither is wrong, but the owner should know the difference before choosing.

For a longer look at each coat type, including bathing and drying, read dog coat types explained.

Why the skin needs care

Dog skin is thinner than human skin and has a different pH, which is one reason shampoos made for people are not recommended for dogs. Thin skin also means it is easy to damage with tools that feel harmless on our own hands.

In practice this means:

• Brushing too hard, or too long in one spot, can leave the skin red and sore. A slicker brush held with a light grip and moved in short strokes does the work without scraping.
• Clipper blades heat up. A hot blade on thin skin can cause a burn, so groomers check blade temperature regularly and swap or cool blades during long clips.
• Close blades on sensitive areas (the belly, the armpits, the inside of the legs and the sanitary area) can cause clipper irritation, so many groomers use a longer blade there, or a lighter touch.
• Trapped moisture matters. A coat that is not dried right down to the skin, especially a dense undercoat, can hold dampness against the skin and contribute to skin problems.
• Skin under mats is often already irritated, because mats pull on the skin and trap moisture and debris. Expect redness underneath a matted coat, and handle that area gently.

Grooming also gives you a regular, close view of the skin, which makes groomers well placed to spot changes early: redness, flaking, parasites, lumps or hair loss. What to do when you find them is covered in lesson 4. For how the same science applies to a matted coat, read how to dematt a dog safely.