This is a randomized controlled human exposure crossover study. Investigators aims to assess the acute effects of high temperature exposure and the underlying mechanisms.

The objective of this study is to study changes in functions of multiple organs under heat exposure, which mainly include changes of cardiac function and lung function. In addition, biological samples such as blood samples, nasal fluid, and urine, etc were collected to explore changes in biomarkers such as complete blood count, liver function, kidney function, and inflammatory indicators, etc. Biochemical analysis and omics analysis were conducted to study the changes of human physiological function caused by heat exposure.

Inclusion Criteria:

1. Chinese nationality（aged 18-30 years healthy males and females）;
2. With ability to read and understand Chinese smoothly;
3. Living in Jinan during the study period;
4. Body mass index ≥ 18.5 and ≤ 28;
5. Normal resting ECG；
6. Normal lung function: i. Forced vital capacity (FVC)≥80% of that predicted for gender, ethnicity, age and height; ii. Forced expiratory volume in one second (FEV1) ≥80% of that predicted for gender, ethnicity, age and height; iii. FEV1/FVC ratio≥80% of predicted values.

Exclusion Criteria:

1. Medications or dietary supplements intake that may alter body temperature during the study period;
2. Individuals who have unspecified illnesses, which in the judgment of the investigators might increase the risk associated with heat exposure will be a basis for exclusion;
3. Subjects with anemia, needle fainting and other signs unsuitable for blood drawing；
4. Subjects with cardiovascular diseases or other chronic medical condition, such as congenital heart disease, pulmonary heart disease, and hypertension, etc;
5. Subjects with a history of major cardio-vascular, respiratory, or nervous system surgery, etc;
6. Subjects with neurologic disorders, such as stroke, traumatic brain injury, epilepsy, and depression;
7. Subjects with allergic diseases, such as allergic rhinitis and allergic asthma, etc;
8. Subjects are pregnant, attempting to become pregnant or breastfeeding;
9. Subjects who are currently smoking (including vaping, hookah and e-cigarette) or have smoking history within 1 year of study (defined as more than 1 pk/yr in the past year) or have a greater than equal to a 5 pack year smoking history;
10. Subjects living with a smoker who smokes inside the house;
11. Subjects who are current drinking or have frequent alcohol use (defined as at least 1 time per week) in the past 6 months;
12. Provisional exclusion criteria, such as acute infection in the past two weeks or taking antibiotics. (Subjects can be enrolled after 2 weeks)

Participants will be informed of the study interventions before providing informed consent but will be masked to the order of exposure (i.e., participants will not know the exposure conditions). Data will be blinded prior to analysis.