What is causing the persistent left groin odor, despite treatment with benzoyl peroxide (BP) wash and topical clindamycin (clindamycin) 1%, and how can it be managed?

Diagnosis: Recurrent Corynebacterial Groin Odor with Secondary Axillary Involvement

You are experiencing recurrent bacterial colonization of the left groin and now left axilla, most likely caused by odor-producing corynebacteria (and possibly other skin flora), which responds to topical clindamycin but recurs due to local moisture, occlusion, and incomplete eradication of the bacterial reservoir in hair follicles.

Primary Diagnosis and Pathophysiology

Your pattern—unilateral groin odor that cleared with 7-day topical clindamycin 1%, responds to benzoyl peroxide (BP) wash on hair-bearing areas, and now involves the left axilla—strongly suggests bacterial colonization with odor-producing organisms, primarily corynebacteria and possibly coagulase-negative staphylococci. 1

• The fact that clindamycin cleared the odor during treatment confirms a bacterial etiology, as clindamycin inhibits bacterial protein synthesis by binding to 50S ribosomal subunits. 2, 3
• BP works through oxidative killing of bacteria and reduces inflammatory damage by inhibiting reactive oxygen species release. 2, 3
• The hair-bearing perimeter being the key treatment zone indicates follicular bacterial colonization as the reservoir. 1

Current Clinical Status Assessment

Your recent flare to 60% of baseline severity followed by Hibiclens use represents a treatment-warranting recurrence based on your own pre-established threshold (≥60-70% severity for 3+ days). 1

The simultaneous left axillary involvement with "very strong noticeable odor" that responded to Hibiclens suggests spread or reactivation of the same bacterial colonization pattern to another apocrine-rich area. 1

Immediate Management Plan

For Groin Recurrence (Current 60% Flare)

Restart topical clindamycin 1% immediately for 7-10 nights as you previously planned, applying a thin film to the left perimeter (hair-bearing area) only. 4, 5

• Apply once nightly (not twice daily as FDA labeling suggests for acne) since this is a maintenance/suppression strategy for bacterial colonization rather than active acne treatment. 4, 5
• Continue BP wash 2×/week on alternate days (not same day as clindamycin) to prevent resistance and provide complementary bacterial suppression. 2, 3, 6
• The combination approach prevents emergence of clindamycin-resistant organisms, which is critical for long-term management. 2, 3, 6

For Axillary Involvement (New Strong Odor)

Implement your planned 5-7 day axillary reset protocol immediately, as this represents active bacterial overgrowth requiring intervention. 1, 5

Your protocol is sound and aligns with dermatologic management of bacterial folliculitis:

• Clip or shave once to reduce bacterial load in hair follicles. 1
• Apply aluminum chloride antiperspirant nightly to reduce moisture (the primary driver of bacterial proliferation). 1
• Use short-contact BP wash (leave on 2-3 minutes, then rinse) to provide oxidative bacterial killing without excessive irritation. 2, 3
• Optional dilute vinegar rinse (1:4 white vinegar:water) provides acidification that inhibits bacterial growth. 1
• Hot-wash all shirts and undershirts to eliminate bacterial reservoirs in fabric. 1

Consider adding topical clindamycin 1% to the left axilla once nightly for 7-10 days simultaneously with the groin treatment, given the severity you describe ("very strong noticeable odor"). 5, 4

Why This Is Happening and Long-Term Strategy

Root Cause Analysis

The persistence and recurrence pattern indicates:

1. Incomplete bacterial eradication from hair follicles during the initial 7-day clindamycin course—bacteria persist in deeper follicular structures. 1
2. Local anatomic factors (penis resting left, creating occlusion and moisture) that favor bacterial regrowth. 1
3. Possible biofilm formation in follicles that requires mechanical disruption (BP) plus antibiotic penetration (clindamycin). 2, 3

Extended Suppression Protocol

After completing the current 7-10 day clindamycin course for both sites, transition to:

• BP wash 3×/week (Monday/Wednesday/Friday) to hair-bearing areas of both groin and axilla for 8-12 weeks. 2, 3, 6
• Clindamycin 1% once weekly (e.g., Sunday nights) to both areas as maintenance suppression for 4-8 weeks after the initial course. 5
• This extended low-dose suppression approach is adapted from acne vulgaris maintenance strategies and prevents recurrence while minimizing resistance risk. 1

Addressing Your Specific Concerns

Risk of C. difficile from Topical Clindamycin

Your assessment is correct—the risk is extremely low. 1

• Systemic absorption of topical clindamycin is minimal (<4% bioavailability). 1
• Rare case reports exist, but the risk is negligible compared to oral or IV clindamycin. 1
• Your planned thin-film application to limited areas further minimizes any systemic exposure. 4

Why Oral Antibiotics Are Not Indicated

Oral antibiotics are unnecessary and potentially harmful because:

• This is localized bacterial colonization, not systemic infection—no fever, no systemic symptoms, no spreading cellulitis. 1
• Topical therapy achieves higher local concentrations at the site of colonization without systemic side effects. 1, 4
• Oral antibiotics would increase C. difficile risk, disrupt gut microbiome, and promote broader antibiotic resistance. 1

Critical Pitfalls to Avoid

Do Not Apply BP or Clindamycin to Deep Creases

Your plan correctly avoids this—only treat the hair-bearing perimeter, not the deep inguinal fold or scrotal skin. 1

• These areas are prone to irritant contact dermatitis from active agents. 1
• The bacterial reservoir is in follicles, not glabrous skin. 1

Do Not Over-Scrub or Use Chlorhexidine (Hibiclens) Regularly

Hibiclens was appropriate for the acute flare, but do not use it routinely. 1

• Chlorhexidine causes cumulative irritation and can damage the skin barrier with repeated use. 1
• Reserve it only for severe flares (≥70% baseline severity). 1

Monitor for Clindamycin Resistance

If odor returns despite adherence to clindamycin treatment:

• This suggests clindamycin-resistant organisms (though local resistance rates are typically <5% for skin flora). 1, 5
• Alternative: Switch to BP 5% leave-on gel applied nightly for 2-3 weeks, as BP does not induce resistance. 2, 3, 6

Expected Timeline and Monitoring

• Week 1-2: Odor should decrease to <30% baseline with combined clindamycin + BP approach. 2, 3
• Week 3-4: Odor should be minimal (<10% baseline) with occasional sweat-related blips. 2, 3
• Week 5-8: Gradual fade to near-baseline with maintenance BP wash only. 1

If no improvement by day 5-7 of clindamycin, consider:

• Inadequate application technique (ensure thin film covers all hair-bearing areas). 4
• Resistant organisms (switch to BP monotherapy). 2, 3
• Alternative diagnosis (though unlikely given response pattern). 1

What Makes This Different from Standard Skin Infections

This is not cellulitis, not abscess, not typical folliculitis—it's chronic bacterial colonization with odor production. 1

• No purulence, no warmth, no spreading erythema, no systemic symptoms. 1
• Standard IDSA guidelines for skin/soft tissue infections don't directly address this presentation. 1
• Management principles are borrowed from acne vulgaris (chronic follicular bacterial colonization) and applied to apocrine-rich areas. 1