Table 2.

Summary of clinical trials investigating the beneficial effects of probiotics on skin disorders.

Probiotic Strain	Type of Study	Regimen	Findings	Clinical Outcomes	Reference
B. longum	66 female volunteers with reactive skin participated in a randomized, double-blind, placebo-controlled trial	Skin application, twice daily for 2 months	↓TEWL	Increased skin hydration and resistance to physical aggression, while limiting skin sensitivity	[41]
L. brevis DSM17250	30 volunteers with xerosis symptoms participated in a randomized, placebo-controlled, double blinded pilot study	Skin application, twice daily for 4 weeks	↑Natural skin microbiota ↓DASI ↓TEWL	L. brevis supported the proliferation of S. epidermidis, resulting in symptom resolution	[43]
L. rhamnosus SP1	20 adult volunteers with acne participated in a pilot, randomized, double-blinded, placebo-controlled trial	Consumption of liquid supplement once daily for 12 weeks, 3 × 109 CFU/day	↓IGF-1 ↑FOXO1	Improvement in skin appearance	[47]
B. infantis 35624	26 adult psoriasis patients and 36 healthy volunteers participated in a randomized, double-blind, placebo-controlled study	Oral administration, once daily for 6–12 weeks (1 × 1010 CFU)	↓CRP ↓TNF-α	Systemic inflammation decrease	[50]
L. plantarum IS-10506	22 children with mild and moderate AD participated in a randomized, double-blind, placebo-controlled trial	Oral administration, twice daily for 12 weeks (1010 CFU/day)	↓SCORAD ↑FOXP3+/IL-10	Th2 adaptive immune response was suppressed resulting in clinical improvement	[53]
L. acidophilus L-92	49 AD patients participated in a double-blind, parallel-group, placebo-controlled study	Oral consumption, once daily for 8 weeks	↓SCORAD ↓eosinophil count ↑TGF-β	Suppression of Th2-dominant inflammation and clinical improvement	[54]
L. johnsonii NCC 533	31 AD patients participated in an open-label, multicenter study	Local application, twice daily for 3 weeks	Stable S. aureus load ↓SCORAD	S. aureus colonization was controlled, followed by local clinical improvement of lesioned skin	[59]
DermaACB	62 consecutive patients with aged skin after fractional CO2 laser treatment	Skin application, twice daily for 2 weeks	↓erythema, swelling downtime	Post-operative inflammation signs were reduced	[74]

TEWL: trans-epidermal water loss; DASI: dry skin area and severity index; CFU: colony forming units; IGF-1: insulin-like growth factor-1; FOXO1: forkhead box protein O1; CRP: C-reactive protein; TNF-α: tumor necrosis factor-α; AD: atopic dermatitis; SCORAD: scoring atopic dermatitis; FOXP3+: forkhead box protein P3; IL-10: interleukin-10; TGF-β: transforming growth factor-β (↑: upregulation, ↓: downregulation).