<Things you should know> Correct knowledge about "contact dermatitis" (1) Explanation of the causes and symptoms of contact dermatitis About contact dermatitis Causes (mechanisms) of contact dermatitis (rash) Types of contact dermatitis List of substances that are likely to cause skin irritation (contact dermatitis) Contact dermatitis, which occurs when something touches the skin, is commonly known as a "rash." Symptoms include redness, bumps, and itching. But why does a rash (contact dermatitis) occur in the first place? And what types are there? We'll explain in detail, supervised by a dermatologist. About contact dermatitis Let's explain what a skin rash is. What is a "rash"? A contact dermatitis is a type of skin inflammation caused by contact with an irritant or a specific substance (such as a plant). It is formally known as "contact dermatitis." Common symptoms include itching, burning, redness, and bumps. Scratching can lead to secondary infections, resulting in blisters and a sore, oozing condition.Causes of skin irritation include certain plants, metals, and topical medications, such as ointments and cosmetics. The difference between a rash and hives. Contact dermatitis is a type of eczema. In other words, contact dermatitis is a subcategory of eczema. Eczema is a general term for skin diseases in which the outermost layer of the skin, the epidermis, becomes inflamed due to external or internal stimuli. Contact dermatitis is an eczematous inflammatory reaction that occurs when the skin comes into contact with some kind of irritant. On the other hand, urticaria (hives) is a skin condition in which a part of the skin suddenly becomes red and raised, sometimes accompanied by itching or a burning sensation, and disappears without a trace after 20-30 minutes, or even 2-3 hours. It is named after the urticaria plant, which is said to cause these skin symptoms when it comes into contact with its leaves. Hives are said to be caused by allergies. Furthermore, they are a type of immediate-type allergy, where the time between exposure to the allergen and the appearance of symptoms is very short. The biggest difference between this and a rash is that the hives disappear without a trace. Main symptoms of a rash Next, let's look at the main symptoms of skin irritation. Examples of general symptoms ■ Turns red ■ Bumps (slightly raised skin) ■ Itching Generally, eczema symptoms begin with redness, followed by slightly raised, bumpy skin. It may also be accompanied by itching and a burning sensation. Examples of worsening symptoms ■ Pus ■ Blisters ■ Sores Furthermore, if bacteria enter the skin through scratching or other means, secondary infections can occur, leading to symptoms such as pus accumulation, blistering, and eventually a sore, oozing state of the skin. Sores can also develop. Sores are a condition where pus or blisters rupture, the epidermis peels off, and the dermis is exposed. Causes (mechanisms) of contact dermatitis (rash) Let's look at the main causes and mechanisms of common skin rashes, following the progression from the onset of symptoms to the onset of symptoms. Something touches the skin directly. First, contact dermatitis occurs when something physically comes into direct contact with the surface of the skin, causing irritation. For example, detergents, rubber, plants, metal objects, cosmetics, and topical medications can all be contributing factors. Nerves in the epidermis sense external stimuli. When these substances come into contact with the epidermis, the nerves in the epidermis sense them in order to protect against irritation. Promotes blood flow and dilates capillaries. Receiving information from these nerves, blood flow is promoted and capillaries dilate. As a result, the skin surface becomes red and the skin temperature rises, which can be felt as a flushing sensation. Plasma leaks out of blood vessels, causing swelling on the skin surface. Subsequently, plasma, a type of blood component, seeps out of the capillaries and accumulates near the skin's surface, causing the skin to swell.Because it causes itching, scratching can lead to bacterial infections and pus formation. These steps can lead to skin irritation.However, the symptoms will vary depending on your physical health, immune system, skin characteristics, and the type of irritant. Types of contact dermatitis There are various types of skin irritation (contact dermatitis). Let's take a look at what each type of dermatitis is like. irritant contact dermatitis Simply put, a rash caused by some kind of irritant (contact dermatitis) is called irritant contact dermatitis, or primary irritant contact dermatitis. This occurs when substances such as chemicals, plants, rubber, metal, detergents, and cosmetics irritate the skin, and the skin's resistance to these external irritants is insufficient. It can occur in anyone. A key characteristic is that symptoms appear immediately upon contact with the substance. Furthermore, symptoms similar to a rash may not be irritant contact dermatitis, but rather caused by a weakened skin barrier function. Allergic contact dermatitis Allergic contact dermatitis is a type of dermatitis that occurs when a person comes into contact with a substance, triggering an allergic reaction. It only occurs in people who have antibodies that cause an allergic reaction to a specific substance. A characteristic feature is that symptoms appear 1 to 2 hours after contact. Systemic contact dermatitis This type of allergic reaction occurs when a causative substance enters the body after a contact allergy has occurred, such as through injection, oral medication, or food ingestion, causing allergic symptoms throughout the body. Common examples include reactions to shiitake mushrooms and mercury. Nickel, cobalt, and chromium can also be contributing factors. contact dermatitis syndrome This is a special type of contact dermatitis in which, despite experiencing a contact allergy, the causative substance remains in contact with the skin without being recognized as contact dermatitis, resulting in a variety of skin inflammations not just in certain areas but throughout the entire body. Diaper dermatitis This is a type of irritant contact dermatitis. It causes rashes in the areas that come into contact with the diaper, especially around the vulva and anus. Causes include irritation from urine and feces, irritation from the diaper, and enclosed environments. It is similar to candidiasis, so differentiation is important. Also, diaper rash can occur not only in babies but also in the elderly. Changing diapers frequently can reduce the likelihood of rashes. photocontact dermatitis This is a special type of contact dermatitis related to light. It develops when a causative substance comes into direct contact with the skin and then changes into a symptomatic substance when exposed to ultraviolet light. There are two types: phototoxic contact dermatitis and photoallergic contact dermatitis, but in most cases it is said to be photoallergic contact dermatitis. ■ What is phototoxic contact dermatitis? This condition is caused by a combination of medications and sunlight. It is primarily triggered by UV-A rays, a type of ultraviolet radiation, and is characterized by immediate onset of symptoms without an incubation period. Common causative medications include psoralen, coal tar, and bergapten. Symptoms mainly resemble sunburn, starting with redness and swelling, followed by peeling skin and hyperpigmentation. ■ What is photoallergic contact dermatitis? This is a photosensitive dermatitis caused by an allergic reaction to sunlight after taking medication. Symptoms mainly include redness and blisters. Medications that can cause this include chlorpramazine, thiazide diuretics, and oral diabetes medications. Areas prone to rashes Skin rashes are more likely to occur in the following areas. Let's also look at the main causative substances for each area. face Cosmetics, pharmaceuticals, perfumes, eyeglasses, plants, sunscreen cream, etc. Around the eyes Eyelash curlers, goggles, eyeshadow/eyeliner, mascara, eye drops, contact lens-related products, etc. Around the mouth Toothbrushing, mask, food (such as mango) ear Earrings, piercings, eyeglass frames, etc. neck Necklaces, cosmetics, perfumes, clothing, etc. armpit Antiperspirants, shaving-related products, etc. limbs Rubber, gloves, leather products, nail polish, metals, pharmaceuticals, etc. Arms, legs, and torso Watches, bracelets, plants, underwear/clothing, body soap, detergents, metals, pharmaceuticals, etc. delicate area Underwear, detergent, sanitary products, condoms, etc. butt Clothing, toilet seats, diapers, etc. List of substances that are likely to cause skin irritation (contact dermatitis) The following substances are likely to cause skin irritation (contact dermatitis): Animals, plants and food Plants, trees, insects, fruits, etc. Chemicals/Metals Metals (nickel, chromium, cobalt, mercury, gold, palladium, etc.), cosmetics, sunscreen, toothpaste, shampoo, soap, hair products, accessories, earrings, glasses, necklaces, clothing, rubber, pesticides, etc. Pharmaceuticals Topical medications (such as fradiomycin, imidazoles, and bufexamax), disinfectants (such as povidone-iodine and benzalkonium chloride), bandages, chemicals, eye drops, etc. Supervised by: Dr. Masako Hirata, Director of My Clinic MejiroMedical Doctor, Board Certified Dermatologist, Japan Medical Association Industrial Physician, International Certified Traditional Chinese Medicine Dietitian. Graduated from Nihon University School of Medicine and worked at Tokyo Medical University Hospital. After retirement, she returned to the front lines of clinical practice, treating over 500 patients daily. Subsequently, in 2003, she opened "My Clinic Mejiro," a specialized outpatient clinic for women, and assumed the position of Chairperson and Director. 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.