Inclusion Criteria:
1. Female, aged 40-50 years, in the perimenopausal transition (defined as menstrual cycle irregularity within the past 12 months but not yet 12 months of amenorrhoea).
2. Clinician-diagnosed acne, defined as the presence of acne symptoms (e.g., comedones, papules, pustules, nodules) or a prior formal diagnosis of acne vulgaris by a healthcare professional.
3. Willing and able to consume a daily oral intervention (2x 65 ml probiotic drinks or skimmed milk) for 8 weeks.
4. Willing and able to provide sufficient blood, skin and stool samples at baseline and end-of-study (Week 8). Participants unable to provide adequate blood sample volumes will not be able to start the intervention.
5. Willing and able to provide a photograph of the facial area, with all images anonymised for study purposes.
6. Able to comply with study procedures, including attending clinic visits at KCL.
7. Have access to a refrigerator at home and be able to store the study product(s) safely after collection (i.e., travel time allows safe storage).
8. Capable of providing written informed consent.
9. Have sufficient proficiency in English to complete study questionnaires and assessments.
Exclusion Criteria:
1. Inability or unwillingness to provide informed consent.
2. Inability or unwillingness to comply with study protocol requirements (e.g., clinic visits, sample provision, daily consumption of study drink)
3. Unwilling to record dietary intakes using handwritten diet diaries
4. Not fluent in the English language
5. Is planning on international travel during the study period
6. Current participation in another interventional clinical trial or having received an investigational/pharmaceutical product within the past 3 months.
7. Known allergy or intolerance to dairy products, skimmed milk, or probiotic drinks containing Lactobacillus species.
8. Currently pregnant, currently breastfeeding or planning to become pregnant in the next 4 months.
9. BMI \<18.5kg/m2 or \> 35kg/m2.
10. No unintentional weight loss greater than 4 kg in the 3 months prior to enrolment.
11. History of substance abuse or alcoholism (alcohol intake \>50 units/week) within the last 12 months.
12. Current smokers, or individuals who quit smoking in the last 6-months.
13. Fasting glucose \>7mmol/l (finger prick test at baseline clinic).
14. Active skin infection requiring systemic antibiotics, antivirals, or antifungals within the past 4 weeks.
15. Major gastrointestinal disease (e.g., inflammatory bowel disease, celiac disease, short bowel syndrome) or history of significant gastrointestinal surgery (excluding appendectomy or cholecystectomy).
16. Known immunodeficiency (e.g., HIV, immunosuppressive therapy, systemic corticosteroids \>10 mg/day prednisolone equivalent).
17. History of malignancy or clinically significant non-malignant skin conditions within the past 5 years (except adequately treated basal cell carcinoma).
18. Serious medical conditions that, in the opinion of the investigator, would compromise safety or interfere with study outcomes (e.g., uncontrolled diabetes, advanced cardiovascular, hepatic, or renal disease, active cancer).
19. Women with a history of severe psychiatric illness that would limit adherence to study requirements.
20. Current use of probiotics, prebiotics, or antibiotics within 4 weeks prior to baseline.
21. Current use of systemic corticosteroids, or other immunosuppressive/immunomodulatory therapies within the past 3 months.
22. Currently receiving, or having received, phototherapy (e.g., UVB, PUVA, laser/light-based treatments, including at home treatments) for any skin condition within the past 3 months.
23. Currently receiving, or having received, systemic dermatology treatments likely to affect skin inflammation or immune response within the past 3 months (e.g., isotretinoin, methotrexate, cyclosporine, biologics such as TNF, IL-17, IL-23 or IL-4/IL-13 inhibitors).
24. Currently receiving, or having received, topical treatments likely to significantly alter skin inflammation within the past 3 months (e.g., high-potency topical corticosteroids, topical calcineurin inhibitors such as tacrolimus or pimecrolimus, topical retinoids, or photodynamic therapy).
25. Currently using, or have used, probiotic skincare (e.g., topical creams and serums) within the past 3 months.
26. Currently receiving, have undergone, or plan to undergo cosmetic skin procedures (e.g., chemical peels, laser therapy, dermal fillers, microneedling) within the 3 months prior to, or within 3 months after the first (baseline) visit.
27. Currently using, or have used, hormonal contraceptives or treatments known to exacerbate acne, including Mirena (levonorgestrel-releasing intrauterine system), oral progesterone-only contraceptives (e.g., mini-pill), and synthetic progestogens (e.g., norethisterone) within the past 3 months.
