Red flags 

The vast majority of cases of shingles are unlikely to be associated with severe complications. However, those involving the eye, nose or ear which relate to cranial nerve involvement, those affecting multiple dermatomes and those with suspected bacterial superinfection need urgent same-day referral.

Immunocompromised patients, including those on systemic corticosteroids or chemotherapy, should also be referred urgently. The key red flags are:

• Any involvement of the forehead, nose or eye (or with visual symptoms). Known as herpes zoster ophthalmicus infection, this affects the ophthalmic division of the trigeminal nerve, which also innervates the eyeball. Hutchinson’s sign (a rash on the tip, side or root of the nose) indicates an increased likelihood of eye inflammation and permanent corneal nerve damage or denervation. However, rarely it presents as an unexplained red eye without an obvious rash. Complications include keratitis, optic neuritis, retinitis, glaucoma and blindness and it requires urgent specialist treatment
• Involvement of the ear. Herpes zoster oticus (Ramsay Hunt syndrome) occurs when the virus affects the facial nerve. The first sign is often deep, severe ear pain. It is characterised by lesions in the ear, facial paralysis
  (Bell’s palsy), and associated hearing and vestibular symptoms
• Shingles in pregnancy. This may need antiviral treatment under specialist care
• A person who has suspected shingles where the rash is severe, widespread, or they are systemically unwell (which may signify more widespread dissemination of the virus)
• Immunocompromised people (see Table 1) and children who have suspected shingles
• Involvement of more than one dermatome
• Superinfection of skin lesions. Secondary infection of the lesions, usually with staphylococcal or streptococcal bacteria, may occur and rarely can result in cellulitis, osteomyelitis or life-threatening complications.

Details about severe complications are available at NICE CKS Shingles