In this study, the effect of dehydration by sauna exposure on the intestinal permeability in 20 healthy subjects is investigated. Participants attend three visits: 1) Sauna visit (to achieve 3% dehydration), 2) Positive control visit (intake of indomethacin which is known to increase intestinal permeability), 3) Negative control visit. At all visits, saliva samples, blood samples, faecal samples, saliva samples are collected and the multi-sugar permeability test is performed. In this test, participants drink a sugar solution and then urine collect urine for 5 and 24 h. The ratio of the sugars detected in the urine by liquid chromatography/mass spectometry is a reflection of the intestinal permeability. Saliva samples are collected for assessment of cortisol, a stress marker. Blood and faecal samples are collected for assessment of markers of intestinal barrier function and inflammation.

Inclusion Criteria:

1. Written informed consent prior to any study related procedures
2. Age > 18 till <50
3. Willing to abstain from probiotic products or medications known to alter gastrointestinal function throughout the study

Exclusion Criteria:

1. Abdominal surgery which might influence gastrointestinal function, except appendectomy and cholecystectomy.
2. Current diagnosis of hypertension.
3. Current diagnosis of psychiatric disease.
4. Over 100kg or with a BMI over 35.
5. Systemic use of steroids in the last 6 weeks.
6. Use of antibiotics or antimicrobial medication in the last month.
7. Daily usage of nonsteroidal anti-inflammatory drugs in the last 2 months or incidental use in the last 2 weeks prior to screening.
8. Usage of medications that could affect the barrier function, except oral contraceptives, during the 14 days prior to screening.
9. Diagnosed inflammatory gastrointestinal disease.
10. Known organic gastrointestinal disease (e.g. irritable bowel syndrome, inflammatory bowel disease, chronic diarrhoea or constipation).
11. History of or present gastrointestinal malignancy or polyposis.
12. Recent (gastrointestinal) infection (within last 6 months).
13. Eosinophilic disorders of the gastrointestinal tract.
14. Current communicable disease (e.g. upper respiratory tract infection).
15. Malignant disease and /or patients who are receiving systemic anti-neoplastic agents).
16. Chronic neurological/neurodegenerative diseases (e.g. Parkinson's disease, multiple sclerosis).
17. Autoimmune disease and/or patients receiving immunosuppressive medications.
18. Major relevant allergies (e.g. food allergy, multiple allergies).
19. Chronic pain syndromes (e.g. fibromyalgia)
20. Chronic fatigue syndrome
21. Regular use of probiotics in the last 6 weeks.
22. Smoking and/or chewable tobacco.
23. Planned changes to current diet or exercise regime.
24. Use of laxatives, anti-diarrhetics, anti-cholinergics within last 4 weeks prior to screening.
25. Use of immunosuppressant drugs within last 4 weeks prior to screening.
26. Women: Pregnancy, lactation.
27. Abuse of alcohol or drugs.
28. Any disease/condition which in the investigator's opinion could interfere with the intestinal barrier function.
29. Any clinically significant disease/condition which in the investigator's opinion could interfere with the results of the trial.

No individual participant data will be shared