Folliculitis: This is an inflammation of the hair follicle, which can appear as a red, pinpoint opening pimple, especially after popping. The mild itch and absence of pain or drainage support this diagnosis.

Infected Sebaceous Cyst: Although the patient denies drainage, an infected sebaceous cyst could present with a red, inflamed appearance and a central opening, especially if it has ruptured.
Abscess: A small abscess could present similarly, although the absence of pain and drainage makes this less likely.
Insect Bite Reaction: Given the itchy nature and the appearance, an insect bite reaction could be considered, especially if the patient has been exposed to insects recently.

Breast Cancer: Although extremely rare for a breast cancer to present as a small, inflammatory pimple, any new breast lesion warrants consideration of malignancy, especially in the absence of typical infectious symptoms.
Mastitis: An inflammatory condition of the breast tissue, mastitis can present with redness, swelling, and sometimes a central opening if an abscess forms. It's crucial to rule out mastitis, especially if the patient is lactating or has a history of similar conditions.

Hidradenitis Suppurativa: A chronic skin condition characterized by recurrent, painful abscesses and nodules, typically in apocrine-gland-bearing areas like the breasts. The absence of pain and the solitary nature of the lesion make this less likely.
Eczema (Dermatitis): Could present with itchy, red lesions, but the pinpoint opening and history of the lesion popping are not typical for eczema.
Keratoacanthoma: A low-grade, or sometimes considered benign, tumor that can resemble a pimple but tends to grow rapidly and can have a central crater-like appearance. It's rare and usually found on sun-exposed areas, but could be considered in the differential for a solitary, growing lesion.

Initial Approach: Clinical evaluation, including a thorough history and physical examination.
Potential Labs:
- Complete Blood Count (CBC) if infection is suspected.
- Imaging (ultrasound or mammogram) if breast cancer or a complex cyst is a concern.
Treatment:
- Folliculitis/Infected Sebaceous Cyst: Topical antibiotics, warm compresses, and possibly oral antibiotics if severe.
- Abscess: Incision and drainage may be necessary.
- Insect Bite Reaction: Antihistamines or topical corticosteroids for itch relief.
- Breast Cancer/Mastitis: Referral to a specialist (oncologist or breast surgeon) for further evaluation and management.
- Hidradenitis Suppurativa: Treatment involves antibiotics, retinoids, and possibly biologics, under the care of a dermatologist.
- Eczema (Dermatitis): Topical corticosteroids and moisturizers.
- Keratoacanthoma: Surgical excision is often recommended.