Acne Severity Grading — IGA Scale
The Investigator's Global Assessment (IGA) scale is a validated tool for grading acne vulgaris severity based on lesion type and count. It provides a standardized 6-point scale from clear (0) to very severe (5).
About
The Investigator's Global Assessment (IGA) scale for acne vulgaris is a static 5-point or 6-point ordinal scale used by clinicians to assess acne severity at a single time point. The IGA evaluates the predominant lesion type (comedones, papules, pustules, nodules) and the extent of involvement. It is widely accepted by regulatory agencies (FDA, EMA) as a co-primary endpoint in acne clinical trials alongside lesion counts. Multiple validated IGA variants exist including the IGA for acne (IGA-A) and the Facial IGA (FIGA).
Formula
Acne severity is determined by lesion type and count. Grade 0-5 based on comedones, papules, pustules, and nodules.
The IGA scale grades acne severity from 0 (clear) to 5 (very severe). Grade 0: Clear skin. Grade 1 (Minimal): Rare comedones, few papules. Grade 2 (Mild): Comedones, some papules and pustules. Grade 3 (Moderate): Many comedones, papules, pustules. Grade 4 (Severe): Numerous pustules, occasional nodules. Grade 5 (Very severe): Highly inflammatory with numerous nodules.
Score Interpretation
Acne vulgaris affects approximately 85% of adolescents and young adults. It can lead to permanent scarring and significant psychological distress. The IGA scale is a FDA-accepted endpoint for acne clinical trials and provides standardized severity assessment for clinical decision-making.
Clear — 0–0
Clear skin, no acne lesions.
Management: Continue maintenance therapy if previously treated.
Minimal — 1–1
Rare comedones, few papules.
Management: Topical retinoid therapy.
Mild — 2–2
Comedones with some papules and pustules.
Management: Topical retinoid + benzoyl peroxide.
Moderate — 3–3
Many comedones, papules, and pustules.
Management: Topical retinoid + topical or oral antibiotic.
Severe — 4–4
Numerous pustules, occasional nodules.
Management: Oral antibiotic + topical retinoid. Consider isotretinoin.
Very Severe — 5+
Numerous nodules and inflammatory lesions.
Management: Oral isotretinoin first-line. Dermatology referral.
Reference Ranges
| Population | Normal Range |
|---|---|
| Acne vulgaris patients | Grade 0 (clear) to Grade 5 (very severe) |
Tabeeb+ Medical Review Team
Expert dermatology review panel.
View medical review board & editorial policy →Example Calculation
A teenager with 30 comedones, 15 papules, 8 pustules, 2 nodules on the face. Lesion count suggests Grade 4 (severe).
Related Conditions
Related Medications
Common Mistakes
Scoring post-inflammatory hyperpigmentation as active acne.
Post-inflammatory hyperpigmentation and erythema are residual changes, not active lesions.
Frequently Asked Questions
When should isotretinoin be considered?
References
- Zaenglein AL, et al. Guidelines of care for the management of acne vulgaris. JAAD. 2016;74(5):945-73.
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