Why won't black spot on wound heal?

It is possible that the black vertical line on the boy's thumb nail is a result of a melanonychia striata, which is a linear nail melanin pigmentation. It is relatively common in children and is generally harmless. However, it is important to have it evaluated by a doctor, especially if it is growing, to rule out any underlying medical conditions.

Having a painful mouth ulcer can be uncomfortable. For some, the first signs of it manifest as a burning or tingling sensation. However, ulcers can also be induced by emotional stress, or injury to the mouth, or even eating certain food types. As a sedative, a gentle mouthwash that does not contain alcohol should suffice for you to clean the area of an ulcer. Besides, it's also possible to glue a pain relief gel or to swallow a tablet for pain relief. Bloating or blistering, which can be caused by spicy or acidic foods, should also be avoided. These foods may exacerbate your ulcer.

It’s normal for your skin not to have an immediate breakout when you quit using a salicylic acid cleanser. Different people have different experiences with purging. A niacinamide serum may be beneficial in clearing your skin. Reducing redness and improving skin texture are some of the things niacinamide can do. Ensure you follow the directions on the package and be patient for results.

The likelihood of HIV infection is negligible if a diabetic needle pricks your hand. HIV is transferred via blood, however, the needle prick is not a high-risk exposure. If you are concerned, watch out for symptoms such as flu, fever, or rash. If you see them, go to a doctor. 

The causes of the cold abscess might include a bacterial infection but tuberculosis is the other explanation. The signs can be a painless lump, the fever, and sometimes sweating at night. It is vital to get a thorough examination and treatment from a doctor who may prescribe antibiotics for a bacterial infection or TB specific medications if needed.