The Sensitive Period for Socialization in Puppies and Kittens

Important building blocks for a behaviourally-healthy cat or dog at the time when it matters most.

A shy puppy hiding under a table on the deck
Let shy puppies hide if they want to. Photo: Anna Hoychuk (Shutterstock)

By Zazie Todd, PhD

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The sensitive period for socialization is a very important time in the lives of kittens and puppies. This is when their brains are especially receptive to learning about the kind of social world they will live in as they get older.

For both kittens and puppies, the sensitive period for socialization is a time when they need lots of positive experiences with all kinds of people and other animals. During this time they will also habituate to anything they might meet in later life (different sounds, surfaces, etc). If they are well socialized during the sensitive period, they are likely to develop into friendly, confident adult dogs and cats.

Sometimes people aren’t sure how to do socialization, so it’s important to note these should be positive experiences in which anything potentially stressful is very, very mild. Bear in mind that anything new is potentially stressful. You can use food to help make positive associations, and insofar as possible give the puppy or kitten a choice. For example, wait for them to approach you instead of forcing yourself on them; let them hide and take their own time to come out if they are shy. This will help to build their confidence. 

The Sensitive Period for Socialization in Puppies

In puppies, the sensitive period begins at 3 weeks and goes on until about 12 or 14 weeks. Our knowledge of this period comes from classic experiments on socialization that involved isolating puppies during this time. We don’t know exactly when the sensitive period ends, and it may end at slightly different times depending on the breed.

This means two things for people who get puppies. First of all, because part of the sensitive period occurs before the puppy comes to live with you, it’s important to ensure you get a puppy from a breeder or rescue where the puppy is in a home environment and getting socialization already. Puppies acquired from pet stores are more likely to have behaviour problems such as aggression, and one reason could be that they are missing those early socialization opportunities because the environment they are born into is typically not a home environment. An early socialization program for puppies means they are less likely to have behaviour problems such as body sensitivity and separation-related behaviours as adult dogs.

Second, it means you have to be prepared to continue socialization during those first few weeks the puppy is with you.

The sensitive period for socialization in puppies and kittens
Photo: Bad Monkey Photography

Sometimes people want to wait until their puppy has had all its vaccinations before beginning socialization. This is understandable, but unfortunately it means they miss this important period. Because the leading cause of death of young dogs (under 3) is euthanasia due to behaviour problems, rather than infectious diseases, the American Veterinary Society for Animal Behaviour recommends that puppies start puppy class at 7-8 weeks of age. Puppies should have one set of vaccinations before the first class, and should also be dewormed.

Choose your puppy class with care to make sure the dog trainer will use reward-based methods. Classes should include socialization opportunities with people and play with the other puppies, not just basic obedience (see: why do dogs play?). Puppy class usually lasts 6 weeks, and one study suggests that a one-off puppy party does not have as many benefits.

Remember it’s your job to take care of your puppy and ensure those experiences are positive. If other people want to pet your puppy, be sure to give your puppy a choice.

The Sensitive Period for Socialization in Kittens

In kittens, the sensitive period for socialization is between 2 and 7 weeks. This is typically before a kitten comes to live in your home, showing how important it is to get kittens from someone who will have socialized them.

We know this from a study by Dr. Eileen Karsh that handled kittens for four weeks from the ages of 3 weeks, 7 weeks, and 14 weeks. When tested at 14 weeks and at regular intervals up to 1 year of age, the kittens that had been handled from 3 weeks of age stayed for much longer when placed on a person’s lap and were faster to approach someone who was sitting at the other side of the room. There's a lovely account of this research in Thomas McNamee's book, The Inner Life of Cats

Research shows that if kittens are handled by 4 – 5 different people during this time, they will be more sociable as adult cats than if only one person had handled them. When kittens are handled and played with by more people between the third and ninth weeks, they are not just more friendly, but people seem to feel a closer bond with them, so it affects human attachment to the cat too.

Just as for puppies, it’s important the handling is a positive experience for kittens. Again, you can give them a choice (let them approach you). Speaking nicely to them while handling is also a good idea.

Even though the sensitive period for socialization will have passed when you bring your kitten home, it’s important to continue to give the kitten positive experiences. This will help them to generalize what they have already learned.

Most people don’t take their kittens to a class, but some places do offer them – it’s called Kitten Kindy® (as in kindergarten). Kitten Kindy® was created by Dr. Kersti Seksel, a veterinary behaviourist in Australia. Maybe your vet will know of a class near you, since these classes are often held at vet clinics. That means there’s a bonus that the kittens will start to have positive experiences at the vet!

The sensitive period for socialization in puppies and kittens

Kitten class is typically for kittens aged 7 – 14 weeks, and is two or three sessions. Kittens should have had their first vaccination and been dewormed.

Kitten classes should include teaching your kitten to like the cat carrier, how to be handled and groomed, and having the nails trimmed and given medication – all useful skills for your cat. Depending on where you live, it might also include teaching kitty to walk on a harness and leash. If the class includes kittens from other litters, then they get the chance to learn to be around other cats (although they will not necessarily interact).
There should also be lots of useful info on how to provide what your cat needs (scratching posts, enrichment, suitable litter trays, toys and playtime, etc), and how to deal with behaviour problems.

Why is it called a sensitive period?

You may also have heard people refer to a critical period for socialization. A critical period means that if the right exposure doesn’t happen during that window, the abilities will never be developed. It has a sharp beginning and end, and is most likely controlled by genetics.

For example, the critical period for vision in cats is from when their eyes open (between 2-16 days) and 3 months. If they are deprived of visual information during this time, some of the cells in their brain responsible for vision will not develop correctly and even die, meaning they will never develop normal feline vision. One of the classic experiments on this deprived kittens of vision in one eye for the first few months of their life. When they restored vision to that eye, the kittens still did not develop binocular vision.

In contrast a sensitive period has a more gradual onset and offset, during which time the brain becomes more sensitive to the right kinds of experiences, and then towards the end of the period it becomes less sensitive.  Exposure to stimuli during this time affects the developing brain and may also increase plasticity. 

Of course, puppies and kittens don't have identical experiences, and perhaps different kinds of exposures will affect the brain in different ways but work towards the same goal. Plasticity of the brain means that it may be possible to still develop in some ways if these exposures happen later than they should have, even if the development will never be quite the same.

It is difficult to define the beginning and end of these periods, although research on neurological development is providing a lot more information.

Early brain development is so important because it provides the scaffolding for further development later in life – something that also applies to human babies.

Humans have sensitive periods too

Sometimes people are surprised by the idea of a sensitive or critical period. It’s useful to know that children also have sensitive periods for development, during which important brain development occurs in response to the child’s environment.

As mentioned above, these early experiences provide the scaffolding for future development. In fact you will often hear people use the analogy of building a wall – if some of those early experiences are missing, it’s like some bricks are missing from the first layers of the wall.

Children’s early life experiences are very important. Babies need to have lots of positive experiences with adults, very little stress and good nutrition to help build a strong brain architecture. 

If they do, then by the time they start school they are in a better position to learn than children who have not had those experiences. Although some stresses (small and brief) are part of normal, healthy development, we now know that chronic stress in early childhood can be very damaging. If you’d like to know more, there is an excellent series of videos from the Center on the Developing Child at Harvard University.

What do you think are the implications of these sensitive periods?

Further reading

My book, Wag: The Science of Making Your Dog Happy, with a foreword by Dr. Marty Becker, is full of tips on how to raise your puppy and care for them right through to the senior years. 

My book Purr: The Science of Making Your Cat Happy tells you more about the sensitive period for kittens, how to set your home up for them, and how to ensure cats of all ages are happy. 

The books Dog Sense and Cat Sense by John Bradshaw are a great read and include chapters on the science of puppy and kitten development. You can read more about the research on socialization periods here, as well as lots of other interesting facts that will help you understand your dog or cat better.

In The Inner Life of Cats, Thomas McNamee talks to Eileen Karsh about her research on kitten development, and weaves the tale of his own cat in with his account of feline science.

Culture Clash by Jean Donaldson is a great introduction to what you need to know to train your dog. The Trainable Cat by John Bradshaw and Sarah Ellis explains how to teach your cat the skills they need to be happy in our world.

You might also enjoy The Boy Who Was Raised as a Dog by Dr. Bruce Perry and Maia Szalavitz, which looks at how psychiatrists and psychologists can use what we know about early human development to help children who’ve been through trauma.

If you’re looking for something academic, these two books cover the early development of dogs and cats (and many other topics besides):

The Domestic Dog: Its Evolution, Behavior and Interactions with People, edited by James Serpell.

The Behaviour of the Domestic Cat by John Bradshaw, Rachel Casey and Sarah Brown.

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This page was last updated in July 2024.

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