Protruding veins on the back of the hand may be caused by excessive vital energy and blood, purple or thin skin, lumbar disc herniation, and digestive tract abnormalities. Here are some reasons:

1. Excessive Vital Energy and Blood

Most people usually hear about the disadvantages of insufficient vital energy and blood, but in fact, excessive vital energy and blood can also have certain negative effects on the body. Excessive vital energy and blood can make a person's temperament more prone to impulsiveness and mania. The prominent veins on the hands are often caused by excessive vital energy and blood.

2. Purple or Thin Skin

Compared to people with dull and yellow skin, the veins on the hands of those with fairer skin are more prominent. This is similar to writing on thin paper versus black paper, where the handwriting is naturally more visible on the thinner paper. Additionally, careful observation can reveal that the veins on the hands of overly frail individuals become more visible when exerting force. This is because these individuals have less body fat, making the prominent veins more apparent.

3. Lumbar Disc Herniation

Some people in traditional Chinese medicine believe that the prominent veins on the hands may be related to conditions such as dampness, phlegm, and toxin-related rashes in the body. Therefore, when the veins on someone's hands are particularly prominent, they may also experience symptoms such as lower back pain and lumbar disc herniation.

5. Digestive Tract Abnormalities

If the veins on the hands extend to the fingertips, it is necessary to pay attention to the digestive tract as there may be abnormalities. Some people may also experience this type of condition when suffering from microvascular circulatory disorders in the head, which are caused by insufficient blood supply to the capillaries in the head. Therefore, it is essential to take this seriously.