Allergic Contact Dermatitis: This is the most likely diagnosis given the patient's history of a similar incident 5 years ago after consuming raw tuna. The symptoms of itchiness, rash, and tiny red bumps are consistent with an allergic reaction. The fact that the patient did not change anything in their diet or environment suggests that the reaction could be due to a specific allergen, such as a food item or a substance they are exposed to.

Urticaria: This condition is characterized by itchy, raised hives that can appear anywhere on the body. The patient's symptoms of itchiness and tiny red bumps could be indicative of urticaria, especially if the reaction is not limited to the area of contact.
Atopic Dermatitis (Eczema): This is a chronic skin condition that can cause itchy, inflamed skin. The patient's history of a similar incident in the past could suggest an underlying atopic tendency.
Food Allergy: Given the patient's history of a reaction to raw tuna, it is possible that they have a food allergy that is causing the symptoms.

Anaphylaxis: Although the patient's symptoms do not seem severe enough to suggest anaphylaxis, it is a potentially life-threatening condition that requires immediate attention. If the patient's symptoms worsen or they experience difficulty breathing, anaphylaxis should be considered.
Stevens-Johnson Syndrome: This is a rare but serious condition that can cause a severe skin reaction, including blisters and lesions. It is often triggered by an allergic reaction or infection.

Erythema Multiforme: This is a rare skin condition that can cause a rash and blisters. It is often triggered by an infection or allergic reaction.
Dermatitis Herpetiformis: This is a rare skin condition that can cause itchy, blistering skin. It is often associated with celiac disease or gluten sensitivity.
Mastocytosis: This is a rare condition that can cause itchy skin lesions and hives. It is often associated with an accumulation of mast cells in the skin.