The Skin … in numbers: 16% of body weight (= largest organ of the human body) Area = 1.8 m² 3 million cells per cm² Epidermis regenerates every 4 weeks Water 70% within the human body vs. 10% water in the top layer of the stratum corneum
The Skin Functions: Barrier between the body and the environment Controlling of moisture movement into and out of the body Mediation of sensory experiences Assistance in temperature control Protection from ultraviolet radiation Synthesis of Vitamin D
How can we study? In vitro In vivo Animal model Human model
COLIPA European Cosmetic Trade Association The testing of cosmetic products is conducted using volunteers from the same population in which they are intended to be marketed in ( e.g. in terms of sex, age, ethnic origin and skin type ). The effect of population diversity on skin irritation. CD 2006:55:357-363
The Provocative Use Test or Open Test l valuable in confirming positive reactions l suspected material is rubbed directly on to normal skin ( anticubital fossa ) twice daily for 1 wk; 3 cm 2 area l no reaction = negative l false negative reaction are common l for contact urticaria : 15-30 min. reading; retroauricular area or outer aspect of arm immediately above the elbow Fisher’s CD; 6th ed.
Comedogenicity Concept Comedogenic Assays : Rabbit ear model ( ultra-sensitive ) An improved rabbit ear model Human model J Am Acad Dermatol 2006;54:3 Arch Derm 1982,118 BJD 1979;100:699 Cutis 1976;17:344
Human Model The test substances are applied under occlusion for one month to the upper part of the backs of young adults, black men who have large follicles The degree of follicular hyperkeratosis Non-invasive “follicular biopsy” techniques Arch Dermatol 1982;118:903.
Human model Human model could be used to evaluate comedogenicity, however the result were dissimilar from those observed in the rabbit ear model. Draelos ZD. J Am Acad Dermatol 2006;54:No3
Human model A percent change from baseline was calculated: degree of microcomedone formation A percent change in micromedone of greater or less than 10% of neg. control : noncomedogenic Draelos ZD. J Am Acad Dermatol 2006; 54:No3
Human model The controversial aspect of any model is definition of the end point Human model has strengths and weaknesses Test material applied under occlusion Selection of prominent of follicular orifice This is but one of many tests used by manufacturers to determine safety Draelos ZD. J Am Acad Dermatol 2006; 54:No3
Comedogenicitiy of Sunscreen UVB & UVA radiation would regularly enhance the formation of comedones when acnegenic substances were applied to the external ear canal of the rabbit Patients who experienced summertime exacerbations of acne were frequently heavy user of sunscreens Arch Dermatol 1982;118: June
Comedogenicitiy of Sunscreen UV dose : Solar-Simulating Radiation two MEDs at wk 1 Monday, Wednesday, Three MEDs at wk 2 Friday Grading scale for the degree of comedone formation from 0 to 4 0 None 1 Slight 2 Moderate 3 Strong 4 Severe Arch Dermatol 1982;118:June
Strategies for skin irritation The assessment of the skin corrosion and skin irritation potential of chemicals and finished product is an essential part of the toxicological evaluation prior to manufacture, transport or marketing Robinson MK. Annal New York Academy of Sciences
Predictive irritancy testing (1) Predictive irritancy testing involves specific tests for the irritant potential of individual chemicals as well as test for individual susceptibility to irritation Irritant dermatitis: Derm Clin
Bioassays of irritation skin Measuring subtle degree of noninflammatory skin damage Transepidermal water loss ( TEWL) Electrical impedance Rates of CO 2 emission Chloride ion flux Irritant dermatitis: Derm Clin
Skin irritation/corrosion potential Animal model Rabbit Draize Test Chamber scarification test Human model Human 4-hour patch test 21-day cumulative irritation test Soap chamber test Modified soap chamber test Cup shake test CD 1996:34:204-212 The irritant contact dermatitis syndrome : Toxicology
Anti-irritants The irritant potential of known eye and skin irritant components of formulating skin care products varied greatly depending on components of the formulation CD 2006;55:148-154
Anti-irritants Goldemberg: Anti-irritants (AIs) “ Agents that used in conjunction with skin or eye irritants, reduces their irritant potential sufficiently CD 2006;55:148-154
Anti-irritants Possible mechanisms of AIs Elimination of irritancy Reduce spread of the irritants: Prevention of complete contact with skin Blocking of skin-reactive sites by oily substances to the skin prior to application of aqueous irritants CD 2006;55:148-154
Anti-irritants AIs as treatment modalities: mechanism Anti-inflammatiory Stabilization of the stratum corneum lipid barrier CD 2006;55:148-154
AIs as Treatment Modalities for Acute Irritation 24-hours Patch Test Cumulative Irritation Model: more relevant for efficacy CD 2006;55:155-159
SPF / UVB MED of the sun screen – protected skin MED of the unprotected skin Minimal Erythematous Dose
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