You should worry about a rash in adults and seek medical attention if you notice any of the following signs:

• The rash covers most or all of your body.
• The rash blisters, turns into open sores, or raw skin.
• You have a fever or feel ill along with the rash.
• The rash spreads rapidly.
• The rash is painful.
• The rash involves sensitive areas such as the eyes, lips, mouth, or genital skin.
• Signs of infection appear in the rash, such as pus, yellow or golden crusts, pain, swelling, warmth, unpleasant smell, redness, purple or brown discoloration, or swollen lymph nodes.
• Difficulty breathing, swallowing, or swelling of lips or eyes occurs, which may indicate a severe allergic reaction (anaphylaxis).
• The rash is accompanied by sudden onset, bruising, purple spots, blistering, or skin discoloration.
• The rash has lasted a week or more or shows worsening symptoms.
• A rash appears alongside systemic symptoms like high fever, severe headache, vomiting, stiff neck, or sensitivity to light, which may indicate serious infection.

These signs suggest the rash could be related to serious infections, allergic reactions, autoimmune conditions, or other medical emergencies that require prompt diagnosis and treatment by a healthcare professional, preferably a dermatologist. If you are unsure or worried about a rash, it is best to consult a healthcare provider for a proper diagnosis and treatment plan.