Why Do We Sometimes Need to Scratch?
One of the commonest causes of an itchy skin is an allergy. The word was coined in 1906 by Professor Clemens von Puquet of Vienna to describe a special state of exceptional sensitivity of the body to certain substances brought into contact with it. Such substances are called allergens, and include furs, feathers, foods, dust, pollens and drugs.
Most people have experienced allergy in some degree at some time, and about 10 per cent of the population show more or less permanent symptoms of allergic illnesses. An allergic reaction is always the same, no matter what has caused it. The reason is thought to be that a process similar to the antibody reaction is set off, not in the bloodstream but on the surface of the body cells.
This allergen-antibody damages the cell walls and sets free a substance called histamine which produces two responses. It allows fluid to escape from the blood vessels into the surrounding tissues and it brings about an involuntary contraction or spasm of certain muscles.
When contact with an allergen is external we develop an itch which may be caused by light, heat, cold, hair or fur. It can also be caused by eating foods such as shellfish, mushrooms and straw berries or by an allergy to some drugs and medicines.
If the allergen is inhaled there may be, as in hay fever, an excessive secretion of mucous, or, as in asthma, a severe spasm of the lung’s air passages. A true allergen is always a protein, a complex substance which forms an essential part of animal and plant tissues, but the abnormal reaction is produced only by a particular substance or group of substances.
Like other defense mechanisms, itching is your skin’s response to potential danger it senses from external stimuli. When those stimuli activate the pruriceptors of special nerve cells called C-fibers, the pruriceptors send itching signals to your brain via the spinal cord.
When your brain senses the itch, what does it tell your body to do? Scratch! The natural reaction to an itch is to scratch it with the fingernails. In many cases, the fingernails will dislodge or remove whatever external stimulus was causing the itching sensation, thereby alleviating the problem.
Scientists have learned that scratching the skin causes a small pain reaction. Typically, the area of skin affected by an itch is quite small. When we scratch the itch, we tend to scratch a much larger area of skin. The pain caused over a larger area of skin distracts from the itching sensation, providing temporary relief.
Recently, scientists have started to study the effect of serotonin on itching. Scientists know that scratching causes the brain to release serotonin, which is a hormone associated with pain relief. Scientists now believe serotonin may also make itching worse, which would finally help to explain why scratching only provides temporary relief and itching can seem worse after scratching.