I am not quite sure whether the mouth sore is related to the the scalp lesions. Red patches and pimples in the scalp may be caused by the following conditions. You can see a dermatologist for help.
1. Lupus on scalp
Red patches on your scalp can appear as a consequence of lupus diseases. This is a chronic autoimmune disorder that is characterized by serious skin damage with a rash on the scalp or any other parts of the body. It can also lead to inflammation of joints, damage to liver, heart, kidney, and lungs.
These conditions occur due to malfunctioning of the immune system that does not distinguish between normal body cell and foreign pathogens in the body. The body immune systems are stimulated to produce antibodies that attack healthy body cells and tissue. This leads to inflammation of the skin with sores.
2. Contact dermatitis
Contact dermatitis is a skin condition that develops from an allergic reaction. The skin of your scalp can develop rashes and sores when it becomes into direct in contact with strange substances that can stimulate an allergic reaction to show up on the affected area.
The common allergens that can induce an allergic reaction on your scalp include hair dye, harsh shampoo, poison ivy or any other hair treatment chemicals. Harsh hair dyes and treatment chemicals can irritate the skin of the scalp to form burns like sores.
3. Seborrheic Dermatitis
Dandruff on the scalp is a symptom of Seborrheic dermatitis. This condition is associated with itchy flaky skin that forms white patches. Also, white or yellow sores that crust over and attached to the shaft of the hair can show up.
The condition can affect anybody regardless of the age. Newborns, toddlers, teens, and adult can show up dandruff on their scalp. The main cause of Seborrheic dermatitis is not clearly known and it is not related to cleanliness. Despite washing your hair with shampoo daily, you might develop Seborrheic sores on scalp.
4. Fungal infection on scalp
Ringworm is a known yeast infection that can affect the scalp to develop itchy white scales and sore on the affected area. If ringworm is not treated, they can advance into red inflammation, loss of hair and scarring on the scalp.
This condition is quite common in infants, babies, toddlers or children. Teens and adults can also be affected by yeast infection on their scalp if they have a weak immune system. Ringworm is highly contagious and it can spread very fast with a population.
5. Head lice
Head lice are parasitic insects that can cause sores on scalp. The parasitic insect on the scalp can cause irritation that you may scratch into open sore. These sores can develop into scabs on scalp when they are infected by bacteria or fungi.
The head lice can spread very fast though direct in contact with the person having it. Head lice is not a vector insect hence they cannot transmit other infection. This insect can be controlled by maintaining high standards of cleanliness.
6. Lichen Planopilaris
Lichen planus or Planopilaris is an infection that causes red, pink or purple bumps on the surface of the skin. The condition can lead to painful sores and loss of hair. The more disappointing thing about this infection is that it can result in permanent scarring on your scalp.
The condition is common to individuals with middle age. Lichen planus on the scalp can stay on your skin even for many years without clearing away. The condition can be managed by the application of corticosteroid creams.
7. Eczema on scalp
Eczema is chronic skin disorder that is associated with red itchy scales on the affected parts of the skin. The scalp can form thick scabs that might itch and cause a discomfort. Other than affecting your scalp, the condition can show up on the neck, face, arms, legs, back or any other parts of your body.
8. Eosinophilic Folliculitis
This is conditions that show up as itchy sores on scalp and on any other parts of the skin on the body. The affected area may develop fluid-filled blisters that ooze out pus. This condition is common to people that are infected with HIV/AIDS.
9. Psoriasis on scalp
Psoriasis is chronic skin infection that can affect different parts of the body including the scalp. This disorder causes thick silvery white or gray scabs that spread all over the scalp. The condition can cause intense itchiness on the head that can cause a discomfort. Psoriasis is an autoimmune disorder that can be treated by a qualified doctor.