Cuppings are good for people cannot handle even a little pressure due to myofascial problem or athletes who get pain in a certain movement.
The other day, a guy who I often see came in and I decided to put suction cuppings on. He has a really thick skin and subcutaneous adipose. When I started putting them on, I felt something is wrong. Cupping sucked only the skin up which usually sucks deeper tissue (at least to me it was not right).
This experience made me look into how the cupping actually works.
What is cupping?
Cupping theory is a form of alternative medicine that cups suck the skin and deep tissue up to break up scar tissue, relax the muscle and connective tissue and improve the blood circulations.
Different cups
Glass with the fire

Plastic with manual suction

Silicone

Methods
Dry
Wet
Cupping facilitates to
- Improve blood circulation
- Remove toxins and waste from the body
- Loosen adhesion of connective tissue
- Stimulate the peripheral nerve system
- Reduce pain and muscle tightness
- Decrease the cholesterol level and lymphocytes (leads to reduce the pain)
- Increase the RBCs (Red Blood Cells)
Conditions cupping is proven effective for
- Neck and shoulder pain
- Headache and migraine
- Knee pain
- Facial paralysis
- Brachialgia
- Carpal tunnel syndrome
- Hypertension
- Rheumatoid Arthritis
- Diabetes
- Asthma
Precautions and contraindications
- Anticoagulation drugs
- Open wounds
- Skin inflammation
- Skin lesion
- Varicose veins
- Bone fracture
- Abdomen during pregnancy
- Fresh surgical scar
- Someone with low energy
- Children under 3
- Cancer
Bruising after the cupping session
Cupping is based on energy pathway called Qi in Chinese medicine. When this pathway is somehow blocked, it causes the illness or disease. Bruising after having cupping treatment means that this energy pathway is not running smoothly. As you continue to receive the cupping therapy, this bruise will become less darker.

Conclusion
Cupping helps improve blood circulation, reduce muscle tightness and pain. There are some conditions proven helpful such as musculoskeletal issue, diabetes and rheumatoid arthritis.
Varicose vein may benefit from cupping, however, there is no research I could find.
If you are interested in having cupping, make sure to see qualified therapists.
References
Al-Bedah, A. M. N., Elsubai, I. S., Qureshi, N. A., Aboushanab, T. S., Ali, G. I. M., El-Olemy, A. T., Khalil, A. A. H., Khalil, M. K. M., & Alqaed, M. S. (2019). The medical perspective of cupping therapy: Effects and mechanisms of action. Journal of Traditional and Complementary Medicine, 9(2), 90–97. https://doi.org/10.1016/j.jtcme.2018.03.003
Rchm, M. I. C. Z. (2014). Traditional Chinese Medicine Cupping Therapy (3rd ed.). Churchill Livingstone.
Aboushanab, T. S., & AlSanad, S. (2018). Cupping Therapy: An Overview from a Modern Medicine Perspective. Journal of Acupuncture and Meridian Studies, 11(3), 83–87. https://doi.org/10.1016/j.jams.2018.02.001
Jadhav, D. K. (2018). Cupping Therapy: An Ancient Alternative Medicine. Journal of Physical Fitness, Medicine & Treatment in Sports, 3(1), 55601. https://doi.org/10.19080/jpfmts.2018.03.555601
Furhad, S., & Bokhari, A. A. (2020). Cupping therapy. StatsPearls, https://www.ncbi.nlm.nih.gov/books/NBK538253/