My Armpit Muscle Hurts : Could It Be Tendonitis ?

You have the feeling that one of your armpit muscle hurts ?

Every month, thousands of people on the web wonder if it could be tendonitis. However, there is no tendonitis that causes pain under the armpits!

That being said, you might be wondering: how can we be so sure? What else could it possibly be? Should I continue to worry?

Perfect timing, I specifically wrote this blog post to address these questions.

Happy reading! 🙂

♻️ Last update : February 2024. Written by Albin Guillaud, physical therapist and PhD in public health
👨‍⚖️ Disclaimer : no affiliate links. Complete disclosure in legal notices.

Is there a tendonitis that causes pain under the armpits?

In case not everyone has read the introduction thoroughly, I’ll reiterate here that:

There is no tendonitis that causes pain under the armpits.

Therefore, if you’re experiencing pain under either of your armpits, you can rest assured it’s not tendonitis. So, there must be another cause…

What could this cause be, you may wonder. What else could create this pain if it’s not tendonitis? Let’s explore what it might be.

Why pain under the armpit if it’s not tendonitis?

Pain under the armpit can manifest for many reasons. So, let’s reiterate that none of these reasons include a possible tendonitis.

Before delving into the various issues that can lead to armpit pain, let’s briefly review some anatomy. (Truly just a tiny bit, I promise.)

A bit of anatomy

The armpit comprises several parts. There’s the axillary space in the center, and all around it, there are different muscles (see image and image caption; the names of the various muscles are provided for information purposes only). And there you have it, the anatomy lesson is already complete!

We can now review the main categories of problems that can lead to armpit pain.

Armpit pain due to muscle injuries

For the armpit in the broad sense (axillary space + surrounding muscles), muscle injuries can cause pain in this area. This can range from simple muscle soreness to tears.

Simple push-ups or pull-ups, for example, can easily cause soreness in this area of the body. As for tears, they can occur in intense sports contexts.

Note that aftereffects of muscle injuries can also be responsible for pain long after the initial trauma. (Anecdote: I suspect having experienced such pain myself in the region of the left armpit for about two years. A pain that would have followed a benign muscle injury during a pull-up exercise without warmup.)

Armpit pain related to skin lesions

There are many possible skin lesions in the axillary space (Urso, 2018). Most of these lesions are likely to cause armpit pain. In general, all these lesions are visible or palpable.

Have you checked or had your skin in this area checked?

Armpit pain related to a problem beneath the skin

A problem beneath the skin can cause armpit pain. For example, this can be:

➡️ a benign tumor of the adipose tissue (fat); this is called a lipoma;

➡️ a problem with the lymph nodes (lymphadenopathy); this type of problem can have many different origins:

• infectious;
• tumoral;
• autoimmune (your own body attacks itself for reasons that are more or less well understood depending on the case);
• still poorly understood.

Note that in principle, none of these problems solely cause isolated pain under the armpit. They are generally associated with other symptoms or anomalies detectable by a well-trained professional.

Among the subcutaneous problems that can cause armpit pain, mention can also be made of a benign tumor of a nerve (neuroma). However, it is very rare for such a tumor to produce pain under the armpit (Mikolajczyk, 2015).

Armpit pain of unknown origin

Some armpit pains may result from health situations that are still poorly understood. This is the case for:

• Post-mastectomy Pain Syndrome (post-mastectomy = after breast removal), especially after breast cancer;

• Axillary Web Syndrome, also after breast cancer surgery (Agostini, 2021).

To remember: many reasons can explain armpit pain. Generally, these pains are associated with other symptoms or anomalies detectable by a well-trained professional.

Tendonitis under the armpits does not exist: how can we be sure?

No one can be 100% sure that it is impossible to develop tendonitis that causes pain under the armpits. However, I am personally sure enough to practically act as if it were 100%. Let’s say I’m 99.9% sure.

You may wonder then: how can we be so sure? Why 99.9% and not 75%? or 50%. This questioning is legitimate. To answer it, I would say first that I have never heard of tendonitis causing pain under the armpits:

• neither during my physical therapist training;
• nor during all my years of professional experience.

Of course, it would be very adventurous to rely solely on this. That’s why I used another method: to see if it has ever been mentioned anywhere in the international medical-scientific literature since the dawn of time (or almost).

To understand the interest of this method, it is necessary to first recall an important fact about us humans: we have a certain tendency to create controversial or even non-existent diseases.

(See in this regard the following two Wikipedia articles: Disease mongering and List of diagnoses characterized as pseudoscience.)

As a result:

• if we don’t talk about such and such health problem in the international medical-scientific literature, even in controversial terms,

• then there is a good chance that it doesn’t exist.

Regarding potential tendonitis causing armpit pain, I found absolutely no trace anywhere. For the most curious, here was my search method.

Exploration of medical-scientific literature: method

To find out if there is any tendonitis that could cause pain under the armpits, I used two search engines:

• Google Scholar (specialized in scientific publications in general);

• PubMed (specialized in medical and biological scientific publications).

I first browsed Google Scholar extensively. This is what I do every time I write a new post. I find Google Scholar a bit more user-friendly than PubMed, so I prefer it for rough searches. However, PubMed has the advantage of being:

• specialized in the field we are interested in;

• more up-to-date.

Furthermore, it is easier to conduct systematic searches in PubMed, and thus to report the results. That’s why I only describe below the details of my method and my results for PubMed. The goal here is primarily to illustrate my approach, rather than to draft a scientific article 🙂

Research of relevant keywords

I began by searching for all pertinent keywords. For this, I utilized MeSH, an intricately organized directory of all medical terms and their variations in English.

Hence, I searched for the equivalents and variations of the words:

• tendinitis ;
• armpit ;
• pain.

Using the keywords

Next, it’s essential to combine these words into the correct search formula:

(tendinopathy OR tendinopathies OR tendonopathy OR tendonopathies OR tendinosis OR tendinoses OR tendonosis OR tendonoses OR tendinitis OR tendinitides OR tendonitis OR tendonitides) AND (axilla OR armpit OR underarm) AND (pain OR pains OR ache OR aches)

A formula like this will help identify all scientific articles containing:

• at least one variant of the word “tendinitis” AND;
• at least one variant of the word “armpit” AND;
• at least one variant of the word “pain”.

After this, all that remains is to examine the results.

Exploration of medical-scientific literature: Results

Thus, we obtained 24 references, as opposed to 105,914 references if we only retained terms related to tendonitis. After reviewing the titles of these 24 references, it’s evident that no article discusses tendonitis causing pain under the armpits.

And that’s how I went about it. If you feel like it, you can replicate the method and check the results. If you find anything, let me know quickly! 🙂

As a general summary for this article:

• Tendonitis causing pain under the armpits doesn’t exist;
• There are multiple possible causes for pain under an armpit;
• Consulting a well-trained professional increases your chances of identifying the cause of your pain and being able to treat it properly.

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If you have any questions, remarks, or experiences to share, don’t hesitate, head to the comments! 🙏

See also : How to Diagnose a Shoulder Tendonitis?

📚 SOURCES

Urso B, Lu KB, Khachemoune A. Axillary manifestations of dermatologic diseases: a focused review. Acta Dermatovenerol Alp Pannonica Adriat. 2018 Dec;27(4):185-191. PMID: 30564831.

Agostini, F.; Attanasi, C.; Bernetti, A.; Mangone, M.; Paoloni, M.; del Monte, E.; Mammucari, M.; Maggiori, E.; Russo, D.; Marzo, R.D.; et al. Web Axillary Pain Syndrome—Literature Evidence and Novel Rehabilitative Suggestions: A Narrative Review. Int. J. Environ. Res. Public Health 2021, 18, 10383. https://doi.org/10.3390/ijerph181910383

Mikolajczyk AE, Sacro YA. Atypical Cause of Axillary Pain. Am J Med. 2016 Feb;129(2):e29-30. doi: 10.1016/j.amjmed.2015.09.010. Epub 2015 Oct 22. PMID: 26475255.