What causes a black to gray spot on the face due to air pollution and how can it be treated?

Facial Hyperpigmentation from Environmental Exposure

This appears to be post-inflammatory hyperpigmentation (PIH) or environmental melasma, which should be treated with a combination approach starting with strict photoprotection (SPF 50+ sunscreen reapplied every 2-3 hours) plus topical therapy using either hydroquinone 4% with tretinoin or a triple combination formulation (hydroquinone 4%, tretinoin 0.05%, fluocinolone acetonide 0.01%). 1, 2

Understanding the Condition

The "black to gray spot" you describe on the face is most likely:

• Post-inflammatory hyperpigmentation (PIH): Excess pigment deposition in epidermal and/or dermal layers following environmental irritation or inflammation from air pollution 2
• Melasma: Gray-brown to blue-black macules or patches in sun-exposed areas, exacerbated by environmental factors 1, 3
• Air pollution particles can trigger inflammatory responses leading to hyperpigmentation, particularly in darker skin types 4

Treatment Algorithm

First-Line Therapy (Start Immediately)

Photoprotection (Essential Foundation):

• Apply broad-spectrum SPF 50+ sunscreen daily 1
• Reapply every 2-3 hours during outdoor exposure 1
• Wear wide-brimmed hats (>3-inch brim) when outdoors 1
• Seek shade during peak UV hours (10 a.m. to 4 p.m.) 1
• Use UV-protective clothing with tight weave fabrics 1

Topical Combination Therapy (Choose One):

• Option 1: Hydroquinone 4% + tretinoin 0.05% applied nightly 1, 2
• Option 2: Triple combination (fluocinolone acetonide 0.01%, hydroquinone 4%, tretinoin 0.05%) for faster results 2
• Option 3: Mequinol 2% + tretinoin 0.01% solution as an alternative 2

Second-Line Therapy (If Inadequate Response After 8-12 Weeks)

Add Chemical Peels:

• Glycolic acid peels every 2-3 weeks 4, 3
• Superficial to medium-depth peels are particularly effective and well-tolerated 4
• Can be combined with ongoing topical therapy 3

Alternative Topical Agents:

• Azelaic acid 15-20% foam or cream daily 3
• Kojic acid preparations 4

Advanced Therapy (For Recalcitrant Cases)

Procedural Options:

• Intradermal platelet-rich plasma (PRP) injections showing 45.67% improvement in pigmentation scores 1
• Microneedling with topical agents (more effective than intradermal injections alone) 1
• Treatment sessions spaced 21 days apart, typically 3 sessions required 1

Monitoring and Maintenance

• Document baseline with serial photographs before treatment 5
• Reassess every 2-3 months with repeat photography 5
• Maintenance treatments may be required every 6 months as this is a chronic condition 1
• Lesions persist for extended periods if untreated, warranting aggressive therapy 2

Critical Pitfalls to Avoid

Common Mistakes:

• Forgetting sunscreen reapplication after 2-3 hours or after sweating 1
• Discontinuing treatment too early—PIH requires prolonged therapy 2
• Using topical steroids alone without depigmenting agents (ineffective for PIH) 4
• Not addressing ongoing environmental exposure to air pollution 4

Important Caveats:

• In darker skin types, hyperpigmentation has more dramatic expression and causes significant emotional distress 4
• Recurrence rates are high without maintenance therapy and continued photoprotection 1
• Avoid dermocorticoid-containing depigmenting preparations that can cause acneiform dermatitis 6

When to Consider Alternative Diagnoses

Obtain skin biopsy if:

• Lesions have unusual morphology (blue-gray dermal pigmentation suggesting lichen planus pigmentosus) 3
• No response to standard therapy after 3-4 months 4
• Concern for melanoma or precursor lesions 7