What the picture shows

Most likely diagnosis: Folliculitis (recurrent bacterial/friction folliculitis of the trunk)

• S. aureus is the most common cause of folliculitis, producing thin-walled pustules at follicular openings that come in crops and heal over a few days, sometimes leaving hyperpigmented marks (which is what those small dark spots likely are) - Andrews' Diseases of the Skin, p. 4648.
• Recurrent folliculitis is more common in people who are obese, sweat heavily (hyperhidrosis), wear tight clothing, shave/wax the area, or have occlusion from waistbands - Roberts and Hedges' Clinical Procedures in Emergency Medicine.
• In young adults with truncal, itchy, monomorphic follicular papules/pustules that don't respond well to antibacterials, Malassezia (Pityrosporum) folliculitis (a yeast-driven folliculitis, common on chest/back/shoulders in young men, worsened by sweat and oily skin) is an important differential - Fitzpatrick's Dermatology, Table 161-4.
• Other differentials to keep in mind: keratosis pilaris (usually on arms/thighs, rough not pustular), acne mechanica/friction acne, and if truly recurrent/boil-like with deeper painful nodules, recurrent furunculosis (deeper S. aureus infection, sometimes MRSA) or hidradenitis suppurativa if lesions are in flexural areas and interconnect - these would need in-person exam to rule out.

Why it recurs

General management (a doctor/dermatologist should confirm exact diagnosis and prescribe)

• Wear loose, breathable cotton clothing; avoid tight waistbands/synthetic fabrics against the area.
• Shower promptly after sweating; keep skin dry.
• Avoid shaving/waxing the affected area until it clears; if shaving is unavoidable, use a clean razor each time and shave in the direction of hair growth.
• Don't pick or squeeze the bumps - this spreads infection and causes scarring/dark spots.

• Antibacterial washes (e.g., chlorhexidine or benzoyl peroxide wash) to the area daily.
• Topical antibiotic (e.g., clindamycin or mupirocin) applied to lesions.
• If Malassezia folliculitis is suspected (itchy, monomorphic, resistant to antibacterials), topical antifungals (ketoconazole/selenium sulfide wash) are first-line, per Fitzpatrick's treatment algorithm.

• If lesions keep recurring despite the above, become painful/deep (boils), spread, or if there's fever - a clinician may take a swab/culture, check for S. aureus nasal carriage (treated with mupirocin nasal ointment plus sometimes a short oral antibiotic course), or start oral antifungal therapy if Malassezia is confirmed.
• Persistent, non-healing, or unusually large/deep lesions should be examined in person rather than diagnosed from a photo alone, since folliculitis, furunculosis, and early hidradenitis suppurativa can look similar early on.

The mechanism

• High protein intake, especially from concentrated sources, raises circulating insulin and IGF-1 (insulin-like growth factor-1). Both hormones stimulate sebaceous glands to produce more sebum and promote hyperkeratinization of the follicle - the exact combination that clogs follicles and triggers folliculitis/acne flares - Fitzpatrick's Dermatology, p. 6574; Dermatology 2-Volume Set 5e.
• IGF-1 specifically has been shown to increase inflammatory markers and sebum production directly in sebocytes (the cells lining hair follicles) - Dermatology 2-Volume Set 5e, "Inflammation in Acne."
• This pathway is best documented for whey protein/dairy rather than chicken specifically - multiple case series and a randomized trial link whey protein supplementation to truncal acne/folliculitis flares in young athletic men, with severity tracking the number of days on supplementation - Andrews' Diseases of the Skin, p. 3416; a 2021 review "Diet and acne: review of the evidence from 2009 to 2020" (PMID 33462816) confirms dairy and high-glycemic-load diets have the most consistent evidence, while lean meat itself has weaker direct evidence.
• That said, individual sensitivity varies a lot. Some patients on high-protein diets overall (not just dairy/whey) report flares, likely through the same insulin/IGF-1 axis, especially if the "protein" meals are also high glycemic-load (fried, breaded, sugary sauces) or heavy overall meals that raise insulin more.

What this means practically

1. Keep a simple symptom diary for 2-3 weeks: note what/how much protein you eat, cooking method (fried/breaded vs grilled/boiled), and when new bumps appear (usually 24-72 hrs after a trigger for follicular flares). This tells you if it's truly the chicken, the way it's cooked, or something else in the meal (oil, sauce, dairy sides).
2. Try moderating portion size rather than eliminating protein entirely - a high-protein, low-glycemic-load diet was actually shown to improve acne biochemical markers in one controlled trial, so it's likely more about total glycemic load and any dairy/whey component than protein itself.
3. Avoid whey protein shakes/bars if you use them, since that has the strongest evidence for triggering trunk folliculitis/acne.
4. Stick with grilled/baked chicken over fried/breaded versions, and watch for high-glycemic sides (white rice, sugary sauces, sweetened drinks) served alongside it.
5. Continue the skin-directed measures from before (breathable clothing, prompt showering after sweating, topical antibacterial/antifungal wash) since diet is only one contributing factor, not a replacement for topical treatment.

Management Plan for Recurrent Folliculitis (Trunk/Flank)

1. General/lifestyle measures (do these regardless of cause)

• Loose, breathable cotton clothing; avoid tight waistbands and synthetic fabrics rubbing the flank area.
• Shower promptly after sweating/exercise; keep the area dry.
• Stop shaving/waxing the area until clear; if unavoidable, use a fresh razor and shave with the grain.
• Don't pick/squeeze lesions - this spreads infection and causes the dark post-inflammatory marks you're seeing.
• Trial the dietary modification already discussed (moderate protein portions, avoid whey shakes, prefer grilled over fried/breaded chicken, lower glycemic-load meals) and track with a symptom diary.

2. First-line topical treatment (start here, run 2-4 weeks)

• Antibacterial wash: chlorhexidine 4% or benzoyl peroxide wash, applied to the area daily, left on for 1-2 minutes before rinsing.
• Topical antibiotic for bacterial folliculitis: clindamycin 1% lotion or mupirocin ointment applied to active lesions twice daily.
• Topical antifungal if itchy/monomorphic and not responding to antibacterials (suggesting Malassezia/Pityrosporum folliculitis): ketoconazole 2% shampoo/cream or selenium sulfide, applied to the area and left on 5-10 minutes before rinsing, several times a week - Fitzpatrick's Dermatology, "Management," p. 3618.

3. If topical treatment fails or lesions are numerous/deep

• Oral antibiotics (bacterial folliculitis, if culture-confirmed or strongly suspected): options like cephalexin 250-500 mg four times daily or dicloxacillin 250-500 mg four times daily for 7-10 days - Dermatology 2-Volume Set 5e, p. 4576.
• Oral antifungal (confirmed/suspected Malassezia folliculitis): itraconazole 200 mg twice daily for 1 day per month for several months, or a short induction course, since the yeast sits deep in the follicle and topical treatment alone may not clear it - Fitzpatrick's Dermatology, p. 3618-3621.
• Consider a nasal swab for S. aureus carriage if recurrences are frequent - carriers benefit from mupirocin ointment to the nostrils twice daily for 5 days, sometimes combined with an antibacterial body wash, to reduce reseeding of the skin - Andrews' Diseases of the Skin, p. 4643.

4. Maintenance (to prevent recurrence once clear)

• Continue the antibacterial or antifungal wash 1-2 times a week as maintenance.
• Keep up the clothing/hygiene measures long term, since friction and sweat are the main recurring triggers here.
• Keep the diet trial going if you noticed a link, and reintroduce foods gradually to confirm the trigger.

5. When to escalate to in-person dermatology review

• No improvement after 4 weeks of topical treatment.
• Lesions become painful, deep, or start forming true boils/abscesses (possible furunculosis, which may need drainage and possibly MRSA coverage).
• Spreading, fever, or lesions clustering into interconnected nodules (rule out early hidradenitis suppurativa).