Across many households, introducing a new cat to resident cats is a common challenge — and one that can significantly influence feline welfare. While experts often recommend slow, structured introductions, surprisingly little is known about what guardians actually do, or how these choices relate to the cats’ first reactions to one another. This study offers one of the most detailed looks to date at how new cats are integrated into multi-cat homes and which early behaviors may predict harmonious relationships or conflict.

Drawing on a representative sample of Danish cat guardians, the authors surveyed 308 people who had brought at least one new cat into a home already occupied by one or more cats. Their goal was to:

• Identify common introduction practices and initial cat reactions; and
• Investigate whether specific methods, such as separation or scent swapping, were associated with positive (affiliative) or negative (agonistic) interactions during the first month.

Most newly introduced cats were young — often under six months of age — while resident cats tended to be adults at least a year old.

Introductions Are Mostly Positive

During the first month, affiliative behaviors were more common than agonistic ones. Curiosity was the dominant response for both new and resident cats. New cats initiated play more often, while resident cats were more likely to hiss.

The authors also found evidence of reciprocity: positive behaviors tended to be mirrored between new and resident cats, and the same was true — though less strongly — for negative behaviors.

The older the resident cats, the less likely they were to display affiliative behaviors. For both new and resident cats, agonistic reactions tended to increase with age.

Introductions Are Either Quick Or Slow

Two clear introduction pathways emerged: immediate or gradual, multi-step cohabitation.

Despite professional recommendations for gradual introduction, more than half (56%) of guardians opted to put the cats together right away. The remaining guardians combined multiple strategies often promoted by behaviorists, such as:

• Keeping the new cat in a room that the resident cat couldn’t access
• Confining the new cat to a cage in a room where the resident cat could roam freely
• Letting the cats meet through a barrier (e.g., a mesh door)
• Feeding or playing with one of the cats while the other could watch through a barrier
• Feeding or playing with the cats in the same room
• Separating the cats for short periods of time (e.g., overnight)
• Allowing each cat to explore the other’s area
• Swapping items (e.g., blankets) between the cats to get them used to each other’s scent
• Using calming pheromones or supplements
• Adding extra environmental resources (e.g., food and water dishes, litter boxes, toys, beds)

Many of these techniques were strongly correlated with one another, suggesting they were typically used as bundled approaches rather than isolated steps. On average, most techniques were applied for roughly a week.

Interestingly, gradual methods were used most often when both cats were under a year old — despite younger cats generally being more socially adaptable.

Age Plays An Important Role In Introductions

A key insight from the study is that the association between introduction method and early behavior depends heavily on age.

Young Cats

For pairs where both cats were under four years old, several recommended techniques — including separation, barrier meetings, scent swapping, and calming products — were associated with more combative behavior. This was most pronounced when both cats were kittens or young adults.

The authors suggest possible explanations:

• Owners may choose these techniques when they anticipate conflict.
• Techniques may be applied after early signs of tension appear.
• Young cats may not require gradual introductions and may adapt better when placed together immediately.

Older Cats

When both new and resident cats were five years of age or older, the pattern reversed. In these households, gradual, structured introductions were associated with more affiliative behaviors.

Techniques linked to positive relations in older cat pairs included:

• Barrier introductions;
• Feeding or playing on either side of a barrier;
• Engaging both cats in play within the same space;
• Introducing new resources; and
• Scent swapping and pheromone use.

Given the small sample size for older dyads, these trends should be interpreted cautiously. However, they align with expert guidance that older cats may struggle more with sudden social changes.

The study highlights that “one-size-fits-all” introduction advice may not apply equally to cats of all ages. While gradual methods may help older cats adjust, young cats might not benefit in the same way — and overly structured approaches may even coincide with more early conflict.

At the same time, the study was unable to determine whether introduction techniques cause agonistic behavior. Owners may select certain strategies because they already expect issues, or they may begin applying them reactively after noticing tension. Still, the data provide a valuable first step toward understanding how real-world practices influence feline social integration.

The authors acknowledge several limitations. They relied on guardians’ memories and didn’t record when the introduction took place, so recall bias may be an issue. They also didn’t track the order or timing of techniques, making causal interpretations difficult. Behavioral intensity (e.g., one hiss versus repeated hissing) wasn’t measured. Furthermore, some behaviors like rough play may have been misinterpreted as agonistic by guardians. Future work using video analysis or longitudinal monitoring could help clarify how early interactions unfold and which specific techniques best promote long-term harmony.

Introducing a new cat is rarely straightforward. This study underscores that early interactions are shaped by complex factors, including cat age, guardian decisions, and the cats’ own temperaments. While many households experience curiosity and friendly behavior, others encounter caution or conflict — and young and older cats may require different approaches to set them up for success.

By mapping real introduction practices and linking them to early behavior, the authors provide a foundation for more tailored, evidence-based guidance. Their findings encourage veterinarians, behaviorists, advocates, and guardians to consider each cat’s age and social history when planning introductions — and to recognize that flexibility, observation, and patience remain essential for helping cats share a home peacefully.