Three groups of subjects will be included: 20 subjects in the healthy control group, 20 subjects in the MDD electroacupuncture (EA) intervention group, and 20 subjects in the MDD waiting-list group (participants will receive no treatment within 4 weeks). The temperature and infrared thermography (IRT) images of the facial acupoints of three groups will be recorded by an infrared thermal-imaging camera. The average facial temperature and acupoints temperature will be analyzed and compared within 3 groups. In addition, the correlation between facial infrared radiation characteristics of MDD patients and emotional changes will be explored. Besides, the relative specificity of the two meridians will be investigated.

Inclusion Criteria:

Inclusion criteria for healthy subjects:

1. Healthy subjects should provide a physical examination report within the last year, which could confirm they had not major systemic diseases, such as cardiovascular, respiratory, digestive, urinary, hematological, endocrine and neurological disease;
2. 18 ≤ age ≤ 60 years, both gender;
3. Subjects have clear consciousness and could communicate with others normally;
4. Subjects could understand the full study protocol and written informed consent is provided by themselves. Note: Subjects who meet the above four items will be included.

Inclusion criteria for MDD patients:

1. Meeting the above diagnostic criteria for MDD;
2. PHQ-9 score of 5 to 14, HAMD score of 21 to 35, and a diagnosis of mild or moderate depression by a specialist; (3)18 ≤ age ≤ 60 years, both gender;

(4) Patients have clear consciousness and could communicate with others normally; (5) Patients could understand the full study protocol and written informed consent is provided by themselves; (6) Those who did not use other therapies other than the basic treatment and this experimental therapy. The basic treatment refers to basic antidepressant medications under the supervision of a specialist. The basic antidepressant medications are Selective Serotonin Reuptake Inhibitors, Serotonin-Norepinephrine Reuptake Inhibitors, Norepinephrine-Dopamine Reuptake Inhibitors, Tricyclic antidepressants, Monoamine Oxidase Inhibitors. Note: Subjects who meet the above six items will be included.

Exclusion Criteria:

Exclusion criteria for healthy subjects:

1. Subjects suffering from mental illness, severe depression, alcohol dependence or a history of drug abuse;
2. Subjects in pregnancy, lactation or menstrual period;
3. Subjects have a fever;
4. Subjects have visible skin damage or scars in the face;
5. Subjects participating in other trials. Note: Subjects who meet any of the above will be excluded.

Exclusion criteria for MDD patients:

1. Patients with bipolar disorder;
2. Patients with schizophrenia or other mental disorders;
3. Patients with severe medical diseases, tumors or diseases of the central nervous system;
4. Patients suffering from severe depressive episode with psychotic symptoms;
5. Suicidal patients;
6. Patients with seasonal depression;
7. Patients with organic depression;
8. Patients with alcohol or drug addicts;
9. Patients using other therapies;
10. Patients in pregnancy or lactation;
11. Patients suffering from cognitive dysfunction, aphasia or other diseases that cannot cooperate with treatment;
12. Patients with pacemakers;
13. Patients who are not suitable for EA. Note: Subjects who meet any of the above will be excluded.