Contagious itching: why we itch when we see others – 03/10/2024 – Balance and Health

It’s perhaps the most maddening feeling there is.

If you prick your finger, you can simply ignore the pain. But try to ignore a ravenous itch. Impossible!

Why does it happen?

Until recently, researchers had only scratched the surface, if you’ll pardon the expression, of itch science. But this is starting to change.

Scientists now know that the sensation of itching is transmitted by a series of specific processes and neurons, which opens the way to a whole new series of treatments.

But why do we itch in the first place?

It is believed that mammals originally evolved the itch sensation as a kind of reflex, which helps us expel invading pathogens and avoid harmful substances in the environment.

But clearly, there is also a psychological aspect to itching that we still don’t fully understand.

One example is the phenomenon of contagious itching, which occurs when people see someone scratching themselves and suddenly begin to itch.

In 2011, professor of dermatology and medical scientist Gil Yosipovitch, from the Miller School of Medicine at the University of Miami, in the United States, carried out an experiment.

He asked healthy witnesses and people with atopic dermatitis — a disorder that causes chronic itching — to watch short videos of people scratching themselves or sitting still. Participants were injected with histamine (a substance that causes itching) or an inert saline solution.

Both groups reported increased itching, but the phenomenon was more pronounced among patients with atopic dermatitis — 82% of them reported increased itching sensations after watching videos of people scratching themselves.

And this phenomenon is not just restricted to human beings.

In 2013, Yosipovitch demonstrated that when adult rhesus monkeys watched a video showing other monkeys scratching themselves, they also began scratching themselves spontaneously. This indicates that they also suffer from contagious itching, like humans.

There’s even evidence to suggest that we and other mammals are hardwired to avoid itchy people. This may be because the act of scratching can be interpreted as a sign of infestation or infection with a parasite or disease.

Physician and neuroimmunologist Brian Kim, from the Icahn School of Medicine at Mount Sinai, in the United States, observed, during a laboratory experiment, that mice tend to move away when they see another mouse scratching itself.

But when a mouse sees another mouse in pain, they try to lick and groom their companion. In other words, it appears that they approach other mice in pain, but move away from those that are itchy.

From an evolutionary point of view, it makes sense. Scientists believe that itching evolved as a way to remove parasites, lice and mites from our bodies, preventing infestations.

There is evidence that scratching provides some protection against infections. In nursing homes, for example, where people are immobile and unable to scratch themselves, scabies epidemics are common.

In other words, people who scratch a lot may inadvertently send a signal to others that they have a transmissible infection.

“I think, instinctively, it’s survival,” says Kim. “I live in New York, and if I go to the subway and see someone scratching themselves, I instinctively tend to walk away.”

“I think it’s programmed into a person’s nervous system that if someone is itching, they may be infested with something that is contagious. But if someone is in pain, the human instinct is to approach that person, it’s the survival of the tribal instinct.”

Perhaps for this reason, people who suffer from chronic itch report feelings of shame, embarrassment, and stigmatization associated with their condition.

Many of them suffer from anxiety and depression, as well as low self-esteem. But unfortunately, stress can exacerbate itching, creating a cycle of itching and anxiety that never ends.

But Yosipovitch says the last thing a doctor should do is tell chronic itch patients to stop scratching. “It’s like telling someone to stop yawning, you can’t, it’s a reflex,” he explains.

But why is scratching something so irresistible?

One theory states that when we scratch, we generate pain signals that are sent to the brain. These signals act as a distraction, reducing the itching sensation, even if it’s for a second.

Scratching also releases the neurotransmitter serotonin, which may be responsible for the pleasant sensation. But the real reasons we feel so good about scratching are complicated and not fully understood.

“There seems to be something about the way the skin senses or transmits information to the brain that prevents it from dealing with too many things in one place at once,” says dermatology professor Marlys Fassett of the University of California, San Francisco, in the United States.

“What happens in people with chronic itching is that they feel pleasure from the act of scratching themselves”, explains the professor.

“Neuroscientists are interested in the pleasure sensory neurons that stimulate the skin, because stopping that pleasurable itch and scratching addiction is a very important therapeutic issue.”

The original text was published here.