Allergic Contact Dermatitis: This is a common condition that occurs when the skin comes into contact with an allergen, causing redness, itching, and bumps. The presence of tenderness and the location over the neck and chest suggest a reaction to something like jewelry, clothing, or a personal care product.

Eczema (Atopic Dermatitis): Characterized by itchy, inflamed skin, eczema can present with red bumps and tenderness, especially if the skin is scratched.
Folliculitis: An inflammation of the hair follicles, often due to bacterial or fungal infections, which can cause red, tender bumps on the skin.
Heat Rash (Miliaria): Caused by blocked sweat ducts, heat rash can lead to red bumps and discomfort, especially in warm, humid environments.
Insect Bites: Bites from insects like mosquitoes, bed bugs, or fleas can cause red, itchy, and sometimes tender bumps on the skin.

Cellulitis: A bacterial skin infection that can cause redness, swelling, and tenderness. It requires prompt antibiotic treatment to prevent serious complications.
Stevens-Johnson Syndrome: A rare but serious disorder of the skin and mucous membranes, often caused by an adverse reaction to medication. It can start with flu-like symptoms and progress to widespread skin lesions and blistering.
Toxic Epidermal Necrolysis (TEN): Similar to Stevens-Johnson Syndrome but more severe, TEN is a life-threatening condition that requires immediate medical attention.

Pemphigus: A group of rare skin disorders that cause blistering of the skin and mucous membranes. While rare, pemphigus can be severe and requires specific treatment.
Kawasaki Disease: An illness that affects children and causes inflammation in the walls of medium-sized arteries throughout the body. It can present with a rash, among other symptoms like fever and swollen lymph nodes.
Erythema Multiforme: A skin condition characterized by target lesions, which can be triggered by infections or medications. It's relatively rare but can be a sign of a significant underlying issue.