Stretch Mark Under Arm: Causes and Care

The underarm contains folds, hair follicles, sweat glands, and skin that moves repeatedly with the shoulder. Growth, muscle or body-size changes, pregnancy, and hormonal influences can stretch the deeper supporting tissue, leaving narrow red, purple, brown, or pale lines. Colour depends partly on your natural skin tone and how recently the marks formed. Stretch marks themselves are not the same as an infection or a reaction to deodorant, although irritation from products can occur nearby.

Keep the fold gently clean and dry, avoid scrubbing, and stop any product that stings or causes a rash. Wear breathable clothing during exercise and avoid shaving over irritated skin. If you want cosmetic improvement, a dermatologist can discuss [Microneedling](/treatments/aesthetic-procedures/microneedling/), [Fractional Laser Treatment](/treatments/laser-and-energy/fractional-laser-treatment/), [RF Microneedling](/treatments/laser-and-energy/rf-microneedling/), or [Carboxytherapy](/treatments/aesthetic-procedures/carboxytherapy/). Underarm skin may need conservative settings and careful aftercare.

Arrange a clinical review if the area is painful, hot, rapidly changing, persistently itchy, bleeding, or draining. A firm lump, marked swelling, or a rash that extends beyond the fold should not be assumed to be a stretch mark. Seek urgent help for fever with spreading redness or facial swelling after a product or procedure.

Ask how the clinician distinguished stretch marks from fold dermatitis, folliculitis, or another skin condition. Discuss pigment changes, treatment depth, friction from clothing, deodorant use, and the aftercare plan for the underarm.