<Things you should know> Correct knowledge about "eczema (dermatitis)" (1) Explanation of the causes and mechanisms of eczema (dermatitis) About eczema (dermatitis) Main causes of eczema (dermatitis) The mechanism of eczema (dermatitis) The difference between eczema (dermatitis) and prurigo Many people have likely experienced symptoms such as itchy, red, inflamed skin or small bumps on the skin. However, did you know that these symptoms are not necessarily "eczema (dermatitis)"? Eczema is defined as inflammation of the epidermis accompanied by itching. Even if there is inflammation on the skin, if it doesn't itch, it's not eczema. We will introduce correct knowledge about "eczema," which many people experience, under the supervision of a dermatologist. About eczema (dermatitis) Eczema is a condition in which inflammation occurs on the surface of the skin, accompanied by itching, but the symptoms vary greatly. Along with itching, the skin may become red, slightly raised, or develop small blisters, among other things, and the causes of eczema are also diverse. Main causes of eczema (dermatitis) Eczema can have a variety of causes. The causes of eczema can be divided into external factors, which are stimuli from outside the body, and internal factors, which are internal factors such as constitution. However, in many cases, external and internal factors influence each other and ultimately lead to eczema, so it is sometimes impossible to identify a single cause. external factors There are three main factors related to external stimuli. A substance that can cause a rash in everyone (primary irritant). Inflammatory reactions occur due to the toxicity of the source of contact itself, and can affect anyone. Examples include chemical substances such as strong acids and alkalis. Anyone who comes into contact with sulfuric acid will develop a rash. Allergic mechanism (allergic) Inflammation occurs as an allergic reaction to substances that come into contact with the skin. For example, this can be caused by lacquer, cosmetics, or metals, but not everyone will experience an allergic reaction. People with metal allergies should be careful, as they may experience allergic reactions not only from jewelry but also from dental metals such as silver fillings and crowns used in tooth treatment. Due to atopic predisposition People with an atopic predisposition develop eczema due to factors such as house dust, mites, and pollen. What is atopic predisposition? Atopic predisposition refers to having an allergic disease (such as allergic asthma and rhinitis, conjunctivitis, or atopic dermatitis) in oneself or a family member, or having a constitution that easily produces IgE antibodies, an immune substance closely related to allergies. It is considered a "constitution prone to developing allergies." Internal factors There are mainly three internal factors involved. age Infants, young children, and the elderly have less sebum secretion in their skin, making it prone to dryness. Their skin's barrier function is also weakened, making them vulnerable to external stimuli and more susceptible to eczema. Allergic constitution/atopic predisposition Eczema is more likely to occur in people with allergic conditions such as allergic rhinitis or bronchial asthma, or in people with an atopic predisposition. Systemic diseases For example, eczema can develop in people with systemic diseases such as kidney disease or diabetes. In these cases, poor blood circulation or metabolic dysfunction of the skin is thought to be involved. Can frequent hand washing cause eczema? While handwashing and alcohol disinfection are very important for preventing infectious diseases, many people suffer from eczema as a result of these habits. Repeated frequent handwashing and disinfection weakens the skin's barrier function, making it more susceptible to external stimuli and creating an environment where irritant contact dermatitis and other skin conditions can easily develop. When washing or disinfecting your hands to prevent infectious diseases, be sure to moisturize to protect your skin's barrier function. The mechanism of eczema (dermatitis) There are various causes of eczema. Let's look at how these causes manifest as symptoms such as itching and inflammation on the skin. Skin irritation, contact with foreign substances, or resulting abnormalities (chemical substances, physical irritation, etc.) The body's immune system tries to defend itself against foreign substances, sometimes attacking them or overreacting. Specifically, it releases chemical mediators involved in itching and inflammation, such as histamine and prostaglandins, to attract immune cells, including lymphocytes, which play a crucial role in immune function. When the immune system overreacts, an inflammatory response occurs. Examples of inflammatory responses - Stimulates the itching nerves → causes itching- Capillaries dilate → Redness occurs- Capillary permeability increases, causing plasma components to leak out → swelling (bumps appear) The inflammatory response continues as white blood cells and lymphocytes release more chemical mediators. The difference between eczema (dermatitis) and prurigo Eczema and prurigo are different conditions.The cause of prurigo is often unclear, but it can develop as a result of scratching, leaving eczema untreated for a long time, or using incorrect treatments.Prurigo is characterized by solitary skin bumps (papules) or nodules accompanied by intense itching. Unlike eczema, it does not spread to other rashes through scratching. Because it is extremely itchy, difficult to treat, and tends to recur if not properly treated, treatment involves using stronger steroids than those used for eczema, or phototherapy using ultraviolet light of a special wavelength called "narrowband UVB." Prurigo can be classified into (1) acute prurigo, (2) chronic prurigo, and (3) special types of prurigo. acute prurigo Formerly known as infantile prurigo, it is common in children and can be triggered by insect bites. An overreaction of the immune system to insect bites or scratching of eczema can lead to acute prurigo, causing extremely intense itching. chronic prurigo One example is polymorphic chronic prurigo, which presents as reddish or brownish, bumpy papules on the waist and thighs of middle-aged and elderly individuals. It is characterized by intense itching and difficulty in treatment. Atypical type of prurigo A special type of gestational pruritic urticarial papules and plaques (Prurigo gestationalis) appears around the third to fourth month of pregnancy, usually after the second pregnancy. However, it improves after childbirth.Furthermore, it's important to be aware of dermadromes, which are pruritic rashes that occur in connection with systemic diseases such as internal organ lesions. Since there is a possibility of leukemia or malignant lymphoma, it is necessary to have a proper examination by a dermatologist. My child got bitten by a mosquito! Why is it so red and swollen? Have you ever been surprised to see your child's mosquito bite swell up into a large, red area? When a child is bitten by a mosquito, the rash is caused by an allergic reaction to substances in the mosquito's salivary glands that enter the body. There are two types of reactions: an "immediate reaction" where the bite causes itching, redness, and swelling immediately, and a "delayed reaction" where there is no immediate reaction, but itching, redness, and swelling occur the following day.While there are individual differences, generally speaking, only delayed reactions occur in infancy, both immediate and delayed reactions occur from early childhood to adolescence, only immediate reactions occur from adolescence to adulthood, and neither reaction occurs in old age.Immediate-type itching occurs right after being bitten and subsides within a few hours, while delayed-type itching can return for one to two weeks after being bitten. There's a reason why mosquito bites on children can linger and swell up for a long time. Supervised by: Professor Tokuya OmiGraduated from Nippon Medical School Graduate School. Visiting Research Professor at Aarhus University and Visiting Professor at Nippon Medical School. Certified Specialist in Cosmetic Dermatology and Laser Treatment by the Japanese Dermatological Association. Certified Specialist in Dermatology by the Japanese Dermatological Association. Certified Specialist in Allergology by the Japanese Society of Allergology. We take care to post accurate information,Please point out any incorrect information. Please submit any comments regarding medical information here. Return to the list of guides categorized by health symptoms.