How and why do dogs recognise when a human has cancer? Here is the scientific explanation

Ferenczi Deborah

2023. July 9 - Photos: Getty Images Hungary

Often, one of the most dangerous diseases of our time is not diagnosed in time. In recent years, however, scientists have discovered that dogs can play a significant role in this process: they can detect the presence of cancer at a very early stage.


Scientific research has shown that dogs can tell whether someone has cancer or not. There are certain smells that are associated with different forms of cancer. These can be present in the urine of patients, in their breath, in their body odour. This means that dogs can smell it at a very early stage.

How can a dog signal cancer?

The dog’s behaviour changes. Unlike before, it can keep sniffing you, even if you push it away, it will continue to sniff you almost violently. It can be a warning sign if it starts licking or biting for no reason. It may also try to get your attention, for example by putting its paws on the same part of your body and barking or whining. But it is also often the case that it simply snuggles up to you more than usual, perhaps following you around.

How do they feel about the disease?

Although doctors use a range of high-tech equipment to detect cancer as early as possible, they have discovered that dogs can be much more effective. They can sniff it out at an earlier stage than some instruments. A new study has shown that dogs can detect the disease with almost 97 per cent accuracy using their highly developed sense of smell.

Research organisations in this field, such as the Working Dog Center at the University of Pennsylvania and Medical Detection Dogs, have found that animals can detect breast cancer and lung cancer by sniffing the breath of patients.

The dogs detected biochemical differences in the breath of the diagnosed cancer and non-cancer subjects. In the case of bladder cancer and prostate cancer, they were able to detect the cancer in the patients’ urine. For colorectal cancer, breath and stool samples helped. For ovarian cancers, sniffing patients’ blood samples and, for cervical cancer, assessing the patient’s biopsy samples helped identify the disease.

Some dogs are trained specifically for this job. They are introduced to the body fluids of cancer patients so that they can smell the characteristic odour on others. Dogs that have not been trained can also smell the difference, but they do not know how to give a clear indication. So they use their body language to try to indicate that something is wrong. If you regularly experience similar signs, consider seeking medical advice.

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