Common causes of armpit pain include muscle strain, infections, allergic reactions and sweat rash. Rare causes include cysts, pinched nerves, autoimmune disorders and cancer.
There seem to be no conditions that would cause pain exclusively in the right or in the left armpit. Pain in both armpits can be caused by menstrual cycle or systemic infections, such as infectious mononucleosis.
Pulled Muscles and Other Injuries
Muscle injuries are one of the most common causes of pain.
Muscle strain (pulled muscle) due to arm overuse or overstretching can cause sudden pain, tenderness and mild swelling in the muscles in the front, behind or below the armpit.
Armpit pain with bruising can be caused by using crutches, wearing splints, direct hit into the armpit, rib fracture, shoulder dislocation or armpit surgery.
Serratus anterior muscle overuse can result in stabbing pain in the side of the chest, shoulder blade and inner side of the arm.
Pectoralis minor syndrome includes pain below the collarbone, in the armpit and upper back.
Long thoracic nerve injury on the side of the chest can result in numbness and vague mild aches below the armpit, and protruding scapula (winged scapula).
Rib fracture usually causes sudden, sharp pain on the side of the chest (below the armpit).
Botox injections in individuals with excessive sweating (hyperhidrosis) can result in constant armpit pain.
Painful Armpit Lumps
Painful armpit lumps can be swollen lymph nodes, which can develop in:
- Infectious mononucleosis (infection by the Epstein-Barr virus)
- Toxoplasmosis, a parasitic infestation contracted by ingestion of cat feces
- Bubonic plague (mainly in Africa) and rat-bite fever (mainly in Asia) are bacterial infections that can cause sudden fever and very tender lymph nodes in the armpits [9,10].
- Bacterial infections:
- Cat scratch disease 
- Tularemia (rabbit fever, deer-fly fever) 
- Staphylococcal (staph) or streptococcal (strep) skin infections (boils, cellulitis and impetigo) [6,7]
- Armpit abscess [13,17]
- Snake, spider or scorpion bite [20,15]
Other painful lumps in the armpits include abscesses and cysts, for example, in hidradenitis suppurativa.
Painful Armpit Rash
Itchy or burning rash in the armpits can be due to:
- Ingrown hair due to shaving
- Ringworm – a fungal infection
- Bacterial folliculitis
- Boil (furuncle) – a bump formed by several infected hair follicles
- Heat rash (sweat rash, miliaria)
- Fox-Fordyce disease – a rare disease with clogged sweat glands
- Irritant or allergic contact dermatitis due to deodorants or clothes
- Erythrasma – a bacterial infection caused by Corynebacterium
- Inverse psoriasis
- Hidradenitis suppurativa – a chronic inflammation and infection of the hair follicles
Armpit Pain in Women
Cyclic breast pain is dull, heavy pain in the upper outer parts of breasts and sometimes, armpits or arms on one or both side; it starts after ovulation and resolves with the onset of menstruation [3,4].
Mastitis is a breast inflammation, usually caused by an infection during breastfeeding. Symptoms include red and swollen breast on one or both sides and enlarged and painful lymph nodes in the armpit on the affected side .
Unlikely Causes of Armpit Pain
The common cold, flu, chickenpox, tonsillitis, scarlet fever, ear infection, tooth abscess, strep throat (pharyngitis), throat cancer (laryngeal or pharyngeal) or thyroid cancer can cause enlarged lymph nodes in the neck, but less likely in the armpits.
Heartburn, angina pectoris or heart attack may cause armpit pain, but not likely without typical pain behind the breastbone or in the upper back.
Hyperthyroidism and hypothyroidism do not typically cause armpit pain.
Fibromyalgia can cause pain in the neck, upper chest and back, but not likely in the armpits.
Skin tags (soft skin stalks) and warts in the armpits are usually painless .
Frequently Asked Questions
Can skin cancer appear in the armpit?
Skin cancer probably very rarely appears in the armpits. However, melanoma on the back can be associated with enlarged lymph nodes in an armpit .
Does any condition cause pain specifically in or near the right or left armpit?
In short, no. Heart-related pain is more common on the left side, but it is more likely felt in the left shoulder or upper arm than in the armpit.
- Mononucleosis MedlinePlus
- Lymphangitis MedlinePlus
- Breast pain Mayo Clinic
- Breast pain (mastalgia) John Hopkins Medicine
- Mastitis while breast-feeding WebMD
- Partridge E, Lymphadenitis differential diagnosis Emedicine
- Axillary (arm pit) lymph node enlargement Doctors Longue
- Swollen lymph nodes Merck Manual
- Narita M, Lymhadenopathy Antimicrobe
- Plague World Health Organization
- Sarcoidosis Cedars-Sinai
- Shrestha D et al, 2013, Systemic lupus erythematosus and granulomatous lymphadenopathy BMC Pediatrics
- Armpit conditions WebMD
- Kitridou R, Swollen lymph nodes due to rheumatoid arthritis? Everyday Health
- Blackman JR et al, 1992, Venomous Snakebite: Past, Present, And Future Treatment Options The Journal of American Board of Family Medicine
- Vaamonde R et al, 1997, Silicone granulomatous lymphadenopathy and siliconomas of the breast PubMed
- Abscess WebMD
- Christiaensen E et al, 2009, Axillary lymphadenopathy as a first symptom of diabetic mastopathy PubMed Central
- Skin Tags and Cysts: When You Should Worry Cleveland Clinic
- Snake Bites John Hopkins Medicine
- Toxoplasmosis NetDoctor
- Cat scratch disease Centers of the Disease Control and Prevention
- Tularemia Centers of the Disease Control and Prevention