Why Do Dogs Kick Their Back Legs When You Scratch Them?

The common behavior of a dog kicking their legs when being scratched is known as the ‘scratch reflex’. It most often occurs when a dog is being scratched behind the ears or, especially, on their belly. It is an involuntary reaction, meaning your dog isn't actively choosing to do it. They are often not aware they are kicking at the air while they are being scratched, giving the impression that the dog is in ecstasy. But is this the case? In reality, the involuntary action is a signal sent by the brain to the leg when they are stimulated in vulnerable regions.

In nature, animals can easily come in contact with parasites, insects, small debris (such as twigs, leaves, thorns, etc.) and dirt. These can stick to their fur or skin and generate discomfort, often in the form of a tingling sensation. By detecting the presence of a foreign body in these sensitive regions, nerve endings under the dog's skin send a message to their brain. This immediately activates the scratch reflex. In doing so, the dog can automatically try to remove foreign bodies, dirt or parasites which can cause them harm. Illnesses, allergies and injuries can therefore be prevented.

For this reason, when we pet or scratch our dogs in sensitive areas, the dog looks like they are kicking the air. The high concentration of nerve endings in these areas means the scratch reflex is more likely to be activated here than on other parts of the body.

Scientifically, the action is activated by spinal neurons. These are nerve cells which send the signals up the spine to the brain. This is why the scratch reflex appears to only occur in vertebrate animals. The scratch reflex also occurs during rest. This is why you can sometimes see a dog kicking their back legs while they are asleep, giving the impression they are dreaming of running.

The complete action of the scratch reflex is relatively unknown. While we know that motor neurons are involved, one study found that there was “no simple correlation between resting receptive field properties and the activity of neurons during the scratch response”^[1]. This means that, although we know neurons are causing the scratching, we are not exactly sure how.

It is important not to confuse the involuntary scratch reflex in dogs with actual scratching. Actual scratching is an active response of the dog to combat an itch or irritation of the skin. When we are scratching or petting a dog, they may activate the scratch reflex and it will usually end when we stop petting. If we are not doing this, but we see the dog scratching, it may be because of an itch.

Scratching due to an itch is usually done with much frequency and is often more intense than the involuntary scratch reflex. Additionally, we can often observe the dog shows annoyance, irritation or signs of stress when affected by an itch. They will still enjoy receiving petting and scratches from their family, but this may also be partly due to relief or distraction from the itch.

If you notice your dog or puppy does not stop scratching, we recommend checking their body for parasites, wounds, injuries or agitated skin. Conditions such as atopic dermatitis or ringworm might be causing the problem and these will need to be treated. This is why you should take your dog to the veterinarian if abnormal scratching persists.

The answer to the above question is dependent on the individual dog. Some dogs do not enjoy being scratched in certain parts of the body. It can cause a sensation due to their nerve endings which they find unpleasant. It is almost a question of whether or not the dog is ‘ticklish’. As with some humans, some dogs will get upset when this occurs, others will find it enjoyable.

To know whether you should keep petting your dog, you will need to be aware of their body language. To do this, you should observe their facial expressions, posture and reactions whenever you pet them in these areas. You should read up on the postures and meanings of a dog's body language and calming signals. You should also be aware of their general behavior on a day-to-day basis. It will not only help you know their state of mind, but improve the bond between you.

If you observe the dog being relaxed and enjoying your pampering, you can continue to share this enjoyable moment with your friend. If you see them become agitated, growling or even showing aggression, these are clear signs, they do not want to be petted there. A dog which is generally suffering from stress or is considered a nervous animal may be less likely to enjoy this type of petting. However, every dog is an individual and it is up to you to know what your pet does or doesn't like.

Just as with us, dogs love certain physical contact with their loved ones and enjoy moments of peace and relaxation. Although they may require a lot of time for physical exercise and play, they are also fans of good naps and sleep is essential for their well-being.

Before knowing where to pet your dog to relax them, you should know that they generally do not like to be tickled, squeezed, clapped hard or manhandled. To provide a moment of calm, they want slow movement petting and gentle strokes. The strokes can be a little harder if you are giving them a scratch or they personally tolerate it, but be aware they may not enjoy it as much as you think. It is ideal to use both the tips of your fingers as well as the palm of your hand and to avoid going against their fur.

Generally, dogs like to be petted:

• The back of their ears
• The base of their neck
• The chest
• Along the spine
• The Shoulders

Get to know where your individual dog likes to be petted. Gauge their response and it will be the best way to have them coming back for more.

While the canine scratch reflex is normal in healthy dogs, there are some rare times when it might be a sign of something else. Dogs such as the Cavalier King Charles Spaniel are predisposed to health conditions such as syringomyelia. This is when a cyst or cavity forms on the spinal cord which affects the communication of neurons to the brain. A study from 2017 suggests that phantom scratching (scratching at something which isn't there) might be caused by “damage in this region [which might] influence the lumbosacral scratching central pattern generator”^[2], i.e. the neurological control of kicking movements.

Other neurological conditions might cause twitching or involuntarily movement of the limbs. Understanding what causes such movement is something which will need to be determined by a veterinary health professional. Also, trapped nerves, muscle strain or psychological anxiety might be the cause of kicking their legs involuntarily. These possibilities are one of the many reasons it is so important to have regular veterinary checkups for your dog.

If you want to read similar articles to Why Do Dogs Kick Their Back Legs When You Scratch Them?, we recommend you visit our Facts about the animal kingdom category.