Your armpit is a sensitive area containing nerves, blood vessels, and lymph nodes. So it’s not uncommon to experience discomfort and pain in the left armpit. This pain can range from mild to severe and is often the result of an infection, inflammation, or irritation. However, more severe cases may be an indication of a serious condition or complication.

If you’re experiencing pain under your left armpit, there could be a number of reasons for the discomfort, including:

Allergic reaction

Deodorants, perfumes, lotions, and body washes are common skin irritants. If you have sensitive skin or known skin conditions, any of these items can trigger a reaction and may cause pain. Other symptoms associated with skin irritation or allergens include:

If you have an allergic reaction from using a cosmetic product or deodorant, stop using it immediately and see your doctor to avoid more serious symptoms.

Shaving

Improper or ineffective shaving can also cause pain under your left armpit. Using blunt blades or dirty blades can increase your risk of infection and lead to hair follicles becoming inflamed. As a result, you may notice small, painful bumps or ingrown hairs.

To avoid this discomfort, always use a clean, sharp blade when shaving. Also, be sure to moisturize your skin to prevent excessive dryness and irritation from friction.

Infection

Bacterial skin infections are known to cause discomfort under your arm. Bacteria thrives in warm, moist environments. As a result, you may experience irritation, pain, or swelling due to a bacterial infection.

Other skin infections may occur as a result of a fungus or a chronic medical condition known as hidradenitis.

Hidradenitis occurs when the hair follicles and oil glands become clogged, specifically under the arms and in the groin. This condition is often described as a severe form of acne. It’s possible that the immune system then overreacts to inflammation, leading to thick scarring and deep skin infections.

Other than pain, you may experience:

  • itching
  • tenderness
  • multiple cysts and boils
  • recurring infections

For common skin infections, your doctor will typically prescribe antibiotics or antifungal medications to treat the condition. With hidradenitis, you’ll likely take anti-inflammatory medications, and doctors often recommend surgery. Antibiotics are reserved for much larger infections.

Muscle strain

If you exercise regularly or are involved in sports, you may have experienced a muscle strain at some point. Weightlifting or participating in contact sports that require your muscles to overstretch can result in some pain and tightness. This pain can occur in your arm muscles and in your armpit area. For minor injuries, the pain typically improves within a week.

If your pain persists for more than seven days and doesn’t improve with stretching and rest, or you notice a painful lump near or around your armpit, schedule a visit with your doctor. Increased pain or a lump can be an indication of a strain or tear that may require medical treatment.

Shingles

Shingles is an infection caused by the varicella zoster virus, the same virus responsible for chickenpox. It causes a painful rash commonly seen on the chest, back, and underarms.

Other signs of this infection include:

  • tingling in the affected area
  • burning or itching
  • blisters
  • intense pain before the rash develops

Treatment requires antiviral medication by mouth to improve symptoms and keep the virus at bay. If your pain doesn’t improve, your doctor may prescribe pain-relieving medications or anti-inflammatory medicines to reduce symptoms in the affected area.

Swollen lymph nodes

You have a number of lymph nodes throughout your body, including the area near your armpit, where they are generally higher in number. The cells within your lymph nodes help to fight infection. If you develop a significant viral or bacterial infection in your body, your lymph nodes can swell and cause pain under your armpit.

Breast cancer

Breast cancer may be another cause of underarm swelling and pain. In its early stages, you may experience few to no symptoms. If cancer spreads outside the breast, it can affect the lymph system, and you may notice a small lump under your arm. These enlarged lymph nodes can cause discomfort.

If you notice any abnormalities on or around your armpit or chest, seek immediate medical attention. Breast cancer can be present even if you don’t feel a lump in your breast. Your treatment options depend on the type and stage of your breast cancer.

Angina

Angina is a condition that causes severe chest pain due to a temporary reduction in blood flow to the heart. The pain occurs because the heart muscle doesn’t receive enough oxygenated blood to keep up with its activity. Symptoms of this condition can cause pain under your left armpit and shoulder as well as:

Treating angina requires treating coronary artery disease with medications or surgery, along with lifestyle changes to manage the condition. Quitting smoking, managing high blood pressure, lowering cholesterol, controlling diabetes, and participating in regular physical activity are all part of the management plan.

Armpit pain caused by minor irritation or muscle strain should subside within a week. However, if the pain is being caused by a more serious health complication or infection, symptoms will continue and extensive treatment may be necessary.

A number of underlying causes can trigger pain under your left armpit. While many will improve on their own, more severe cases may require medical intervention and even surgical procedures.

Don’t self-diagnose armpit pain, especially with fever or swollen lymph nodes, which can be signs of a serious medical condition. Discuss your symptoms and treatment options with your doctor to ensure you receive the best care.