Photopatch Test

Photopatch Test

Photopatch test is a method of diagnosing and studying photoallergic contact dermatitis (PACD) and other sunlight-induced dermatological diseases through the detection of contact photodamage, which plays an important role in clinical diagnosis and treatment. CD Formulation, as a professional cosmetic service and product supplier, can provide a variety of efficacy tests, safety tests, and so on. Based on our professional laboratory and staff, we can provide you with photopatch test. Photopatch test, as a commonly used cosmetic safety test, can detect this potential possibility to ensure the safety of cosmetic use.

Photopatch Test Principle

The basic principle is to apply the photo allergen to the skin for a period of time, and then irradiated by a certain wavelength of light, the photo allergen, under the action of light energy, makes the first half-antigen into a half-antigen, and combines with the skin proteins to form a full-antigen, which stimulates the body to produce antibodies or cellular immune response. When the sensitized individual is exposed to the same sensitizing factor or cross-sensitized substances again, the body produces a series of metamorphic reactions, with erythema, papules, blisters and other reactions visible to the naked eye, so as to judge the skin's photoreactivity to photoallergens.

It is mainly used to diagnose the etiology of photoallergic contact dermatitis and to determine the photo allergens that cause the reaction. Like the patch test, the patch test is also a skin excitation test, and can also induce irritant dermatitis, therefore, if there is a history of contact urticaria or even a systemic severe allergic reaction of rapid-onset contact reaction patients, can not use the photo allergens that can cause allergic reactions.

Testing Procedure

Step 1 - Apply the photochromic patch: fill the IQ core chamber made of polyethylene plastic with the allergen to ensure complete contact with the skin; then apply 2 identical copies of the allergen on each side of the back, avoiding the scapula and the midline, avoiding the acutely exuding skin, with one side as the irradiated side and the other as the control side, with an interval of at least 3~5 cm between them, and mark the marking with a marker pen.

Step 2 - Remove the allergens after 24 or 48 h of exposure and observe whether there is a simple contact allergic reaction. The irradiated side was irradiated with UVA 5 J/cm2 or less, and the control side was protected from light. After irradiation, both sides were covered with waterproof aluminum foil.

Step 3 - 24, 48, and 72 h after irradiation, observe the reactions on both sides, including erythema, papules, edema, and blisters, and indicate the intensity of the reaction with a scale of 0 to 4.


In addition to the usual precautions for the patch test, the following points should be noted for the light patch test:

  • There should be a large enough area of normal skin on the back for the test, and the test site should be free of inflammation, hyperpigmentation, scarring and other conditions that are not suitable for the photomacular patch test;
  • Patients who have taken photosensitizing drugs such as thiazides and fluoroquinolones should avoid the test, and the time of discontinuation can be decided according to the half-life of the drug;
  • The test should be avoided if the skin disease is in the acute active stage;
  • The test should be avoided if there is clinical suspicion of photoallergic dermatitis caused by systemic drugs;
  • Subjects should not take glucocorticoids 2 weeks before and during the test, and it is advisable to discontinue antihistamines for the first 3 d and during the test.
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