HRIPT testing - 深圳市普威国际检测认证有限公司

The HRIPT (Human Repeated Insult Patch Test), i.e., the Human Repeated Insult Patch Test, is a classic skin safety testing method used to evaluate the potential sensitization (particularly delayed-type contact allergic reactions) of products that come into direct contact with the skin, such as cosmetics, skincare products, and detergents.

Core Purpose

Differentiate between product "irritation" and "sensitization":

Irritation: Direct physical/chemical damage to the skin caused by the product (e.g., erythema, stinging, typically appearing rapidly after contact and dose-dependent);
Sensitization: An immune system response triggered by product ingredients (a Type IV hypersensitivity reaction), requiring repeated contact to "induce" immune system sensitization; allergic symptoms (e.g., erythema, papules, vesicles, etc.) appear only upon re-exposure and are related to the individual's immune status.

Test Procedure

HRIPT is typically divided into 3 phases and must be conducted on healthy volunteers (with no skin diseases and no history of allergies), with a sample size generally requiring at least 50 subjects (or 100 under certain standards):

Induction Phase (Sensitization Induction)

3-4 times per week, patches containing the test product are applied to the skin on the volunteer's back or inner upper arm (dosage adjusted according to product type), with each application lasting 24-48 hours, repeated at intervals of 1-2 days.
Continues for 2-3 weeks, aiming to allow the skin to repeatedly contact potential allergens and induce a sensitized state in the immune system.

Rest Phase

After induction, product contact is discontinued for a 10-14 day rest period to allow the immune system to complete the establishment of "sensitization memory."

Challenge Phase (Allergic Reaction Verification)

The test product is reapplied to the volunteer's skin (usually a new, previously unexposed site), removed after 24-48 hours, and then observed for 48-72 hours (in some cases extended to 1 week).
If a clear allergic reaction occurs (e.g., erythema + papules, vesicles), it is determined as "sensitization positive," indicating that the product may pose a sensitization risk.

Result Interpretation

According to the International Contact Dermatitis Research Group (ICDRG) or relevant standards (such as the EU Cosmetics Regulation and China's Safety and Technical Standards for Cosmetics), skin reactions are graded as follows:

Negative (no reaction);
Doubtful reaction (mild erythema);
Weak positive (definite erythema + mild papules);
Strong positive (erythema + papules + vesicles/exudation).

Importance and Applications

HRIPT is one of the key tests in the pre-market safety assessment of cosmetics and personal care products, particularly for products intended for long-term or repeated use (e.g., facial creams, shampoos). This test can screen for potential sensitizing ingredients, reducing the risk of contact dermatitis in consumers after product use, and complies with cosmetic safety regulatory requirements across various countries (e.g., following the EU ban on animal testing, human tests such as HRIPT serve as one of the important alternatives).

In summary, HRIPT scientifically evaluates a product's sensitization potential by simulating the process of "repeated contact - immune sensitization - re-challenge," and is a core testing method for ensuring the safety of products that come into contact with the skin.