What causes super dark underarms?

The underarm is a warm, folded area exposed to rubbing, sweat, hair removal, and cosmetic products. Irritation can leave Post-Inflammatory Hyperpigmentation after a rash or injury has settled. Intertrigo can cause soreness, redness, moisture, odour, or itching. Colour that feels velvety and also appears on the neck or groin should be assessed rather than treated only as a cosmetic concern.

Clean with lukewarm water and a mild, fragrance-free product, pat dry, and wear breathable clothing. Avoid aggressive scrubbing, lemon, bleaching products, and applying strong acids immediately after shaving. Stop a deodorant that burns or causes a rash. After active irritation is controlled, a clinician may discuss Hydroquinone Treatment, Chemical Peel, Laser Toning, or Laser Hair Removal; these options can also irritate skin if used without a diagnosis and suitable settings.

Arrange medical review for sudden or spreading darkening, a thick velvety texture, persistent itch, pain, scaling, discharge, or a rash that fails to settle after removing a suspected irritant. Get urgent help for rapidly spreading redness, severe pain, fever, or facial swelling. A clinician can check for Intertrigo, Post-Inflammatory Hyperpigmentation, contact allergy, or another cause.

Is this colour change from inflammation, friction, or another condition? Should I change deodorant or hair-removal methods? Would Hydroquinone Treatment be appropriate for me? Which procedure is least likely to trigger more pigment?