Itches the knee when bending

Itching: what's behind it, what helps

What is itching?

Itching, also known as pruritus, is one of the most common symptoms that affect the skin (sometimes the mucous membrane). In 2010, 13 percent of all age groups in Germany were affected at the time of a survey. The need for scratching, rubbing and rubbing is sometimes almost insatiable and excruciating.

Experts know well over a hundred causes of the discomfort. If the skin is itchy, the advice of various specialists is often sought. This is especially true if the itching does not go away after six weeks of treatment. Then there is a chronic pruritus.

There are two main forms:

  • The itching occurs on altered areas of the skin, so it is itching in the case of a suspected skin disease: a case for the dermatologist. Skin diseases are leading causes of itching.
  • The itching occurs initially on "normal" skin. Dry, mature skin is more prone to itching. Severe scratching can damage the skin (technical term here: prurigo nodularis). If you suspect illness, you should first involve your family doctor. He can consult other specialists, such as an internist, neurologist or psychiatrist, to clarify the symptom. Since there are numerous possible causes, diagnosis and therapy can be tedious.

What can relieve the itchiness

Different medications often complement each other well when it comes to taming an itch. In addition to the use of lipid-replenishing and moisturizing agents (basic therapy) and adequate hydration, skin doctors recommend creams or lotions with menthol, camphor, lidocaine or polidocanol for short-term relief. These can temporarily calm or numb the nerve fibers in the skin that cause itching and pain. Zinc-containing pastes can help with itchy rashes in skin folds.

Ointments or creams containing cortisone are often used for application to the skin, and certain antihistamines are sometimes used for external or internal use. Antihistamines inhibit the effects of histamine. This is an endogenous substance that plays an important role in inflammation and causes itching. If the itching disturbs sleep, an antihistamine may be useful, which can make you tired as a side effect. If these strategies don't work, doctors use special drugs for application on the skin or internally, including cortisone.

Of course, the treatment depends as much as possible on the cause. However, it can sometimes take a few weeks for an itch to respond to therapy. If the time seems too long to you or if the itching is still severe, talk to the doctor again.

For further reading

Dry skin: causes and tips

If the skin feels dry, tight and itchy, external and internal influences play a role ...

Itching with allergies, pseudoallergy, contact with animal poison

Although the skin is a protective barrier to the outside world, it is also irritable and vulnerable. Obviously, what causes itching often comes from the environment. We tolerate many substances that we encounter well, others challenge our tolerance. In the event of a conflict, the body mobilizes highly active messenger substances, including the previously mentioned histamine. The tissue hormone is one of the strongest mediators of itching in the body. Histamine occurs to a significant extent in the skin, mucous membranes and nerve cells. It is mainly stored in so-called mast cells.

An allergy arises when an actually harmless substance makes the immune system sensitive (sensitized) and causes it to form special antibodies. The trigger turns into an allergen, the defense substance into an antibody. The next time they come into contact, both connect with each other and often with mast cells. They then release their highly active substances, especially histamine. Traces of the allergen are sufficient for this. The reaction is an "immediate type" allergy. There are other types of allergies, such as the frequently occurring contact allergies, which arise somewhat differently (see interactive graphic).

Certain components in food or pharmaceuticals can, if the person concerned is predisposed, directly - without sensitization and antibody formation - cause the mast cells to suddenly open their floodgates. Then there is a pseudo-allergic reaction. Their strength usually increases with the amount of trigger. Sometimes the breakdown of histamine in the body is disturbed because the enzyme responsible is missing or blocked. If, for example, too much histamine gets into the body through a food, acute reactions are also possible. There are also other types of pseudo-allergic reactions.

Allergy-like reactions can occur on contact with nettle poison, for example from the stinging hair of the oak processionary moth or tentacles of certain jellyfish (animal poison reaction).

For example, whether there is an allergy or a pseudo-allergy cannot be determined from the symptoms alone. The skin begins to itch acutely and a rash can form (technical term: rash). It is best to see a doctor as soon as possible. This also applies if wheals (hives, urticaria) develop or if swelling occurs in deeper layers of the skin - a so-called angioedema (previously: Quincke's edema), for example on the face. In the latter, however, itching is usually absent. The doctor decides whether treatment is necessary immediately and, if so, whether it is an outpatient or must be in a clinic.

If there is swelling in the airways with shortness of breath or circulatory weakness, there is an immediate danger to life: Regardless of what is or could be the trigger: Alert the emergency doctor here immediately (emergency service: emergency number 112). A specialist allergological examination is essential for a more precise diagnosis and treatment of suspected allergies and pseudo-allergies. This also applies to check to what extent preventive measures are promising. Examples of allergies, pseudo-allergies and animal poison reactions with subsequent itching.

Food as a trigger for itching

Usually it is natural ingredients or additives such as colorings or preservatives in certain foods that can trigger a pseudo-allergic intolerance reaction. Well-known candidates are ripe cheese, fish, sauerkraut, red wine (contain, among other things, histamine), yeast, bananas, tomatoes, chocolate, tea, coffee. Hot spices or flavor enhancers such as glutamate are also possible. One of the most common food allergies is cow's milk protein allergy in young children.

Discomfort can occur on the skin (itchy rash, similar to neurodermatitis; see below), in the digestive tract (vomiting, stomach ache) or in the airways (shortness of breath). They range from minor to severe, rarely up to a shock reaction.

The good news for cow's milk protein allergy: Most children tolerate milk gradually and are often as good as symptom-free by the time they start school. The allergy tendency itself (atopy), however, remains.

Chicken eggs, fish, shellfish, soy, hazelnut and peanut are also on the "allergy index". Atopic diseases such as hay fever (pollen allergy), allergic asthma and neurodermatitis increase the risk of also having an allergic reaction to food. Examples: allergy to birch pollen and apple or hazelnut. Symptoms: There may be a furry feeling on the lips and in the mouth and throat. This often leads to diarrhea, nausea and abdominal pain. With pronounced reactions, itchy skin wheals can occur. Breathlessness and circulatory problems are emergencies (see above).

Medicines as a trigger for itching

[] Whether pseudo-allergy or allergy - drugs can also trigger corresponding reactions. Without further investigation, the differentiation is often not easy or impossible. Experience has shown that drugs such as some antibiotics, antidepressants, hormone preparations or anti-inflammatory agents (such as NSAIDs, i.e. non-steroidal anti-inflammatory drugs such as ibuprofen or diclofenac) are more often responsible for allergies.

Drugs such as acetylsalicylic acid (anti-inflammatory drugs), antimalarials, ACE inhibitors (heart and blood pressure drugs), opiates (pain relievers), and X-ray contrast media are sometimes behind a pseudoallergic drug reaction. Even with certain cancer treatments, for example with some biologicals (antibody therapy), pseudoallergic reactions with itching can arise.

Often different skin rashes develop, so-called drug eruptions. This usually happens within a few days to eight weeks after starting therapy. Symmetrical red spots, sometimes distributed like a map, can appear all over the body, often interspersed with specks or nodules, with and without itching. Raised or blistered, severely itchy redness (wheals, hives) are also possible. Occasionally, when taking a drug, itchy changes occur only in certain areas, such as the face, hands and feet. If the drug is taken again after a break, the same places react again.

The first signs of a severe drug reaction can be a fever above 38.5 degrees Celsius, difficulty breathing and swallowing, reddening and swelling of the face, and possibly swelling lymph nodes (so-called pseudolymphomas).

Lyell's syndrome is particularly feared: skin blisters that peel off, severe fluid loss, poor circulation, fever. This severe form of drug allergy is occasionally seen with the use of anti-epileptic drugs, certain antibiotics, anti-inflammatory drugs (NSAIDs), the pain reliever metamizole, or the gout drug allopurinol.

Call the emergency doctor immediately in the event of pronounced or severe symptoms!

Allergies and other intolerance reactions can also occur after the application / contact of various agents on / with the skin, be it drugs, disinfectants, plasters, cosmetics, deodorants and others (see section "2. Itching: Typical skin disease?" Below, keywords " Eczema "and" allergic contact eczema ").