S. thermophilus is a probiotic strain used in cheese and yogurt production. According to preliminary research, it can improve skin health, support immunity, alleviate GI symptoms, and more. However, available clinical evidence is scarce. This post reveals the potential benefits and side effects of Streptococcus thermophilus.
What is Streptococcus thermophilus?
Streptococcus thermophilus is a thermophilic probiotic bacterium traditionally and widely used as a starter in manufacturing dairy products such as cheese and yogurt.
At birth, S. thermophilus is among the first colonizers of the GI tract and may impact the maturation and homeostasis of the intestinal epithelium after birth .
Along with other probiotic bacteria, it regulates the immune response and inflammation via a number of different cytokines such as:
- IFN-γ [2, 3, 4]
- TNF-α [5, 6, 7]
- IL-6 [5, 7, 6]
- IL-1β 
- IL-2, IL-5 
- IL-8 
- IL-10 [8, 2, 3]
- IL-17 [9, 4]
Health Benefits of S. thermophilus
No valid clinical evidence supports the use of S. thermophilus for any of the conditions in this section. Below is a summary of up-to-date animal studies, cell-based research, or low-quality clinical trials which should spark further investigation. However, you shouldn’t interpret them as supportive of any health benefit.
1) Skin Health
Ceramides play an essential role in the barrier and water-holding functions of healthy skin. A significant increase in skin ceramide levels was observed in 17 healthy subjects after treatment with a cream containing S. thermophilus .
Topical treatment with an S. thermophilus-containing cream increased ceramide levels and hydration in the skin of 20 healthy elderly women .
The same treatment increased ceramide levels and improved the signs and symptoms of atopic dermatitis (i.e. redness, scaling, itching) in 11 patients .
The above trials lacked control groups and had small samples, so we should take their results with a grain of salt.
Animal and Cellular Research (Lacking Evidence)
No clinical evidence supports the use of S. thermophilus for any of the conditions listed in this section. Below is a summary of the existing animal and cell-based studies; they should guide further investigational efforts but should not be interpreted as supportive of any health benefit.
2) Lactose Intolerance
Along with L. delbrueckii, S. thermophilus improves lactose digestion in the gastrointestinal tract and reduces the symptoms of lactose intolerance, according to a study on mice .
In one study, S. thermophilus partially alleviated mucositis (inflammation of mucous membranes) induced by chemotherapy in rats .
However, in another study, no protective effects were observed .
It partially prevented weight loss and slightly improved mucositis induced by doxorubicin (chemo) in rats .
S. thermophilus significantly reduced intestinal mucositis severity in rats treated with a chemotherapy drug, 5-Fluorouracil .
Long-term aspirin use may cause gastritis. S. thermophilus reduced inflammation and prevented chronic gastritis in studies on aspirin-treated mice [2, 3].
In studies on mice with ulcerative colitis, scientists observed the potential of S. thermophilus to [17, 9]:
- Increase hematocrit and hemoglobin concentrations
- Improved acute colitis and intestinal lesions
- Suppress the Th17 immune response
6) Antibiotic-Associated Diarrhea
The use of antibiotics increases the risk of C. difficile infection, which can result in diarrhea, colitis, and more serious complications .
Mice infected with C. difficile and treated with viable S. thermophilus had reduced weight loss, diarrhea, and toxin levels .
7) Folate and Hemoglobin Levels
Folate-rich fermented milk produced by high-folate-producing S. thermophilus increases hemoglobin levels in mice .
S. thermophilus exerts an anti-inflammatory effect by suppressing the Th17 response in white blood cells .
S. thermophilus stimulated macrophage and T-cell cytokine production in another cell-based study .
It promoted epithelial cell regeneration and immunological defense mechanisms in human stomach cells .
9) Oral Health
In test tubes, S. thermophilus inhibited the growth of P. gingivalis and reduced the emission of volatile sulfur compounds that can cause bad breath .
10) Probiotic Growth
S. thermophilus is used in the production of yogurt alongside Lactobacillus delbrueckii ssp. bulgaricus. These two species are synergistic. S. thermophilus provides L. d. bulgaricus with folic and formic acid, while L. d. bulgaricus provides amino acids and peptides for the growth of S. thermophilus .
S. thermophilus also improves the viability of L. brevis in milk .
Side Effects and Safety Precautions
S. thermophilus is widely used in the dairy industry and is considered safe for consumption.
However, probiotics should be avoided in immunocompromised individuals, people with organ failure, and dysfunctional gut barrier, where they may cause infection .
S. thermophilus can produce low amounts of biogenic amines: histamine and tyramine. Hence, people with histamine intolerance should avoid probiotics and fermented foods [25, 26].