This is a randomized controlled human exposure crossover study. Investigators aims to assess the acute effects of low-temperature exposure on respiratory health and the underlying mechanisms.

The investigators will conduct a randomized controlled human exposure crossover study among about 40 healthy young adults in Shanghai, China. Each subject will be exposed twice: once to the low temperature (15℃) and once to the moderate temperature (22℃) in a chamber for about 2 hours. During the exposure session, each subject will be requested to rest. Health examinations will be conducted immediately prior to exposure, during the period of exposure, and after exposure. Health examinations include lung function tests and exhaled breath test. Investigators plan to collect blood, pharyngeal secretion, exhaled breath condensate and urine samples.

Inclusion Criteria:

• Living in Shanghai during the study period;
• Body mass index > 18.5 and ≤ 28;
• right-handed;
• receiving or having received higher education;
• with the ability to read and understand Chinese smoothly.

Exclusion Criteria:

• Smoking and alcohol abuse;
• Current drug and dietary supplements intake;
• Subjects with allergic diseases, such as allergic rhinitis, allergic asthma, and atopy;
• Subjects with cardiovascular diseases, such as congenital heart disease, pulmonary heart disease, and hypertension;
• Subjects with respiratory diseases, such as asthma, chronic bronchitis, and chronic obstructive pulmonary disease;
• Subjects with chronic diseases, such as diabetes, chronic hepatitis, and kidney disease;
• Subjects who have a history of major surgery due to the cardiovascular, cerebrovascular, respiratory, or neurological diseases;
• Subjects with neurologic disorders, such as stroke, traumatic brain injury, epilepsy, and schizophrenia;
• Abnormal spirometry (FEV1 and FVC ≤ 75% of predicted and FEV1/FVC ≤ 0.65);
• Subjects with color vision disabilities.