This is a randomized controlled human exposure study. Investigators aim to investigate the products of ozone-sebum reactions and their acute effects on skin health of healthy young adults.

The investigators will conduct a randomized, controlled human exposure study involving 40 healthy young adults in Shanghai, China. Each participant will have both forearms simultaneously exposed-one in a clean air chamber and the other in an ozone chamber-for 2 hours. The ozone concentration at the ozone chamber inlet will be maintained at 200 ppb. The temperature and relative humidity in both chambers will be maintained at 27±2℃ and 45%±5%, respectively. Health examinations will be conducted at three time points: immediately before exposure, immediately after exposure, and 24 hours after exposure. These examinations will include skin measurements and sampling.

Inclusion Criteria:

• Living in Shanghai during the study period;
• Having healthy skin conditions on both forearms.

Exclusion Criteria:

• Subjects with a history of smoking and alcohol abuse;
• Subjects with a regular use of medication and dietary supplements within 2 months prior to enrollment;
• Subjects with severe skin diseases, such as atopic dermatitis, eczema, or severe acne;
• Subjects with allergic diseases, such as allergic rhinitis, allergic asthma, or atopy, or history of allergic reactions within 2 months prior to enrollment;
• Subjects with cardiovascular diseases, such as congenital heart disease, pulmonary heart disease, or hypertension;
• Subjects with respiratory diseases, such as asthma, acute or chronic bronchitis, or pneumonia;
• Subjects with chronic diseases, such as diabetes, chronic hepatitis, or kidney disease;
• Subjects with cutaneous abnormalities on forearm, such as severe pigmentation, multiple nevus, or tattooing;
• Subjects who underwent cosmetic intervention on forearms within 2 months prior to enrollment, such as whitening treatments, UV exposure therapies, depigmentation procedures, or tanning;
• Females in pregnancy or lactation status.