Is annoying eczema caused by sensitive skin or skin allergy?

Patients with eczema are often seen in the clinic. Doctors suspect that it is caused by some cosmetics allergy. When patients ask, "I used it once a few days ago and nothing happened. How could it be the culprit of this allergy?" Or they come to see a doctor for facial eczema and ask, "Doctor, do I have sensitive skin?"
Skin allergies and Sensitive muscle" are two different concepts, but they overlap and affect each other at some levels, so they can be confusing. In fact, as long as you understand them clearly, you will know how to avoid and treat them.

Sensitive skin is prone to contact dermatitis, and daily necessities may be the culprit
Sensitive skin refers to a skin condition that is easily affected by internal/external factors (emotions, stress, diet, sun exposure) and causes dryness, redness, or flaking. Congenitally sensitive skin includes atopic dermatitis and rosacea; acquired sensitive skin is related to improper skin care, such as incorrect face washing methods, lack of sun protection, moisturizing, or age changes.
Skin allergy refers to an inflammatory reaction caused by the skin coming into contact with specific allergens or irritants. For example, contact with strong acids/alkalis or long-term contact with detergents can cause "irritant" contact dermatitis; or repeated exposure to chemicals, fragrances, preservatives, metals, etc. can cause "allergic" contact dermatitis, which can be seen as redness, swelling, itching, peeling and other inflammatory reactions similar to eczema.
However, clinically, people with "sensitive skin" are more susceptible to irritation and "contact dermatitis" than people with normal skin.
Many allergens in life are often the culprits of "allergic contact dermatitis", such as nickel, latex, Peru essence, paraphenylenediamine, etc. Common culprits are as follows:
1. Nickel: It is the most common allergen and is often found in earrings, necklaces, watches and belt buckles. When the nickel contained in these accessories causes allergies, dermatitis will occur in the earlobes, back of the neck, wrists, and around the navel. Therefore, doctors can determine the accessories and allergens that may cause allergies based on the location of eczema.
2. Latex: Some people may experience skin inflammation and blisters after contact with latex gloves or latex products, or even have an immediate allergic reaction due to inhaling latex protein suspended in the air. The structure of latex protein is similar to certain components of fruits such as bananas, avocados, kiwis, chestnuts, and peaches. Therefore, people who are allergic to latex may also easily develop allergic reactions after eating these fruits, which is called latex-fruit syndrome.
3. Peruvian essence: It is a composite resin containing a variety of compounds. It smells like vanilla and cinnamon and is often used in perfumes, skin care products or food as a flavor enhancer. Tomatoes, spices (vanilla, cinnamon, cardamom, cloves) and citrus fruits also contain ingredients of Peruvian essence. Therefore, people who are allergic to Peruvian essence should also pay attention to allergies when eating the above foods.
4. p-Phenylenediamine: p-Phenylenediamine, abbreviated as PPD, is a common ingredient in hair dyes. The darker the color of the hair dye, the higher the PPD content may be, which can easily cause dermatitis at the hairline, ears, back of the neck, and even eyelids.

Where is the problem with the skin? The suspected allergen can be inferred based on the location
In addition to analyzing the ingredients, we can also infer possible allergens from the location where allergic dermatitis occurs:
1. Scalp: Common scalp allergens come from hair dyes, perms or shampoos. However, since the scalp is relatively thick and has a strong resistance, allergic dermatitis often occurs at the hairline, ears, back of the neck or eyelids (flowing to the face when rinsing hair).
2. Eyelids: Allergic to ingredients in mascara, eyeliner, eye shadow, and nail polish (touching eyelids with fingers after applying nail polish).
3. Lips: lip balm, lipstick, lip gloss, nail polish, toothpaste, dental floss, mouthwash, and essence.
4. Neck: jewelry, perfume, nail polish.
5. Underarms: deodorant, antiperspirant.

When our body first encounters an allergen in allergic contact dermatitis, the immune cells in our body will be activated and will have a memory of the allergen, but will not immediately trigger an allergic reaction. This process is called "sensitization," and it takes about 10 to 14 days. When we come into contact with the same allergen again, our body will react to the allergen, producing symptoms of dermatitis such as redness, swelling, scaling, and itching.
This is like when your home is robbed for the first time, you start to be on guard. When the thief comes back the second time, you react immediately and arrest the thief because of your previous experience and preparation. So if you used a certain cosmetic product before and it was fine, you can't conclude that it is not the culprit for the current contact dermatitis!
If you suspect you have contact dermatitis, you can stop using the suspected product to avoid being exposed to the allergen again, and seek treatment from a dermatologist as soon as possible. Doctors can also use the "patch test" (note) to help diagnose the product that causes the allergy, so that patients can clarify everything as soon as possible.
Note: In the patch test, various suspected allergens are dropped onto small patches and applied to the back to observe the skin's reaction in order to determine the culprit causing the allergy.