Redness
This symptom is often accompanied by physical swelling and hotness of the shoulders. Bursitis (inflammation of the bursa sacs) is the most common cause [6] of redness. It is also accompanied by pain and a limited range of motion. There is a myriad of causes of shoulder pain, such as arthritis, torn cartilage, rotator cuff tear, swollen bursae, swollen tendons, bone spurs, pinched nerves, fractured scapula or arm bone, adhesive capsulitis, dislocation, and cardiovascular problems.
References:
[1] https://www.mayoclinic.org/diseases-conditions/rotator-cuff-injury/symptoms-causes/syc-20350225#:~:text=Show%20transcript-,The%20rotator%20cuff%20is%20a%20group%20of%20muscles%20and%20tendons,and%20reduced%20range%20of%20motion.
[2] https://www.versusarthritis.org/about-arthritis/conditions/shoulder-pain/#:~:text=The%20rotator%20cuff%20is%20a,tendons%20of%20the%20rotator%20cuff.
[3] https://www.sports-health.com/blog/understanding-different-types-shoulder-pain#:~:text=Burning%20pain,sensation%20or%20a%20dull%20ache.&text=You%20may%20also%20feel%20radiating,entire%20reason%20for%20your%20pain.
[4] https://www.versusarthritis.org/about-arthritis/conditions/shoulder-pain/#:~:text=Subacromial%20bursitis%20causes%20pain%20and,allows%20bones%20to%20move%20freely.
[5] https://www.health.harvard.edu/pain/how-to-release-a-frozen-shoulder#:~:text=Frozen%20shoulder%20(also%20called%20adhesive,time%20if%20it’s%20not%20treated.
[6] https://www.cedars-sinai.org/health-library/diseases-and-conditions/b/bursitis-of-the-shoulder.html#:~:text=of%20the%20body.-,Bursitis%20of%20the%20shoulder%20(impingement%20syndrome)%20occurs%20when%20there%20is,the%20things%20that%20cause%20pain.