Red bump on back I have a red size of penny .25 inch bumped up hurts when touch it. right the spine line between shoulder blades.what is it?

It is difficult to determine the exact cause of the red bump on your back without a proper examination. Here are a few possible causes:

1. Boil: A boil is a skin infection caused by bacteria, typically Staphylococcus aureus. It starts as a small, red, and tender bump that can grow larger and fill with pus. Boils are common in areas where there is friction or sweating, such as the back.

2. Pimple: A pimple, also known as a spot or acne, is a common skin condition that occurs when the pores of the skin become clogged with oil, dead skin cells, and bacteria. Pimples can appear as red, swollen bumps on the skin and can be painful to touch.

3. Folliculitis: Folliculitis is an infection of the hair follicles. It can cause small, red, and tender bumps to develop on the skin, often with a white or yellow center. Folliculitis can occur anywhere on the body, including the back.

4. Cyst: A cyst is a sac filled with fluid or other material that can form under the skin. Sebaceous cysts, which are caused by blocked oil glands, are common on the back. They typically appear as smooth, round, and movable bumps under the skin.

5. Insect bite or sting: Insect bites and stings can cause red, swollen, and painful bumps on the skin. If you have recently been bitten or stung by an insect, this could be the cause of the bump on your back.

6. Skin cancer: In rare cases, a red bump on the back could be a sign of skin cancer. If the bump is growing rapidly, changing in shape or color, or bleeding, it is important to see a doctor for evaluation.

If you are concerned about the red bump on your back, it is recommended to consult with a doctor or dermatologist for proper diagnosis and treatment. They can examine the bump, determine the cause, and provide appropriate treatment options.