Why does sprayed cat urine emit such a strong smell?

A new study from Iwate University in Japan has examined why sprayed cat urine emits a particularly potent smell compared to urine found in litter boxes.

The phenomenon of spraying, where cats mark their territory by depositing urine on vertical surfaces, presents a significant challenge for cat owners due to the odor’s intensity. 

While previous studies have argued that sprayed urine might contain extra compounds from the anal sac secretions or other sources, definitive scientific proof for this hypothesis has been lacking. 

Compounds in sprayed urine 

The research team undertook a meticulous comparison of the chemical makeup of volatile organic compounds in sprayed urine, standard urine, and urine extracted directly from the bladder using ureteral catheters.

The analyses revealed an unexpected level of chemical similarity across these different types of urine within individual cats. 

Behavioral studies complemented these findings, showing that cats could not differentiate between the smell of sprayed urine and the scent of urine left in the bladder after spraying.

This indicates that the sprayed urine originates from bladder urine without supplementation with chemicals from other secretory glands.

Investigating the underlying mechanisms

This discovery prompted the researchers to shift their focus and investigate alternative reasons behind the distinct pungency of sprayed urine. 

A step forward in understanding this phenomenon was the discovery that cat urine samples easily adhered to the inner surface of plastic syringes when they moved the samples into glass vials for urinary volatile analyses.

“This observation prompted us to explore the underlying mechanisms,” said study lead author Reiko Uenoyama, an expert in animal behavior and biochemistry at Iwate University. 

New theory about the smell of sprayed urine

Previously, Miyazaki discovered a urine protein called cauxin, which was a significant breakthrough in understanding how certain sulfur-containing odorants responsible for the unique “catty” smell are produced. 

“Generally, the wettability of a liquid on a solid surface increases as the surface tension decreases. Based on this knowledge, we hypothesized that the high protein concentration in cat urine might reduce the surface tension of cat urine, enhancing the emission of urinary volatile compounds from the large vertical surface area that was spread over the urine,” Uenoyama said.

Adherence to vertical surfaces

The researchers’ hypothesis was confirmed as they found that the presence of cauxin indeed lowered the surface tension of urine, which in turn increased its wettability and adherence to vertical surfaces. The experts drew a comparison between cat urine containing proteins and a control solution containing albumin, highlighting the unique properties of cauxin in influencing the urine’s properties. 

During their examination, the researchers noted that the unique smell associated with cat urine was identifiable in an artificial small-scale garden, designed to resemble natural settings, where a block sprayed with male cat urine has been placed.

On the other hand, this distinct odor could not be discerned in another garden setup where the same urine had been directly applied to sandy soil and subsequently concealed.

“The difference in environmental odors between the two gardens, despite using the same urine sample, can be explained by most of the urinary volatile chemicals being trapped in the porous structure of the sandy soil. This phenomenon did not occur in the urine adhering to the surface of the block,” explained Miyazaki.

Additionally, liquid droplets of sprayed urine can easily dry on the surface of the block, resulting in greater emissions of volatile chemicals from the scent mark rapidly as compared to from normal urine.”

The urinary protein cauxin is key

Thus, the unique composition of cat spray comes directly from the bladder and does not include substances from other bodily secretions. Nonetheless, this spray is characterized by a notably strong odor due to its ability to adhere better to vertical surfaces. 

The presence of the urinary protein cauxin is key in this process, as it not only generates odorants specific to cats but also amplifies the release of volatile compounds from the urine by lowering its surface tension, thus making it spread more easily. These insights could offer new approaches to mitigating the pronounced scent linked with cat spraying.

The study is published in the Journal of Chemical Ecology.

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