Rash

Differential diagnosis

Common causes of rashes include:

• Food allergy
• Medication side effects
• Anxiety
• Allergies, for example to food, dyes, medicines, insect stings, metals such as zinc or nickel; such rashes are often called hives.
• Skin contact with an irritant
  • Fungal infection, such as ringworm
  • Balsam of Peru
• Skin diseases such as eczema or acne
• Exposure to sun (sunburn) or heat
• Friction due to chafing of the skin
• Irritation such as caused by abrasives impregnated in clothing rubbing the skin. The cloth itself may be abrasive enough for some people
• Secondary syphilis
• Poor personal hygiene Uncommon causes:
• Autoimmune disorders such as psoriasis
• Lead poisoning
• Pregnancy
• Repeated scratching on a particular spot
• Lyme disease
• Scarlet fever
• COVID-19 (see )

Conditions

Diagnostic approach

The causes of a rash are numerous, which may make the evaluation of a rash extremely difficult. An accurate evaluation by a provider may only be made in the context of a thorough history, i.e. medications the patient is taking, the patient's occupation, where the patient has been and complete physical examination.

Points typically noted in the examination include:

• The appearance: e.g., purpuric (typical of vasculitis and meningococcal disease), fine and like sandpaper (typical of scarlet fever); circular lesions with a central depression are typical of molluscum contagiosum (and in the past, small pox); plaques with silver scales are typical of psoriasis.
• The distribution: e.g., the rash of scarlet fever becomes confluent and forms bright red lines in the skin creases of the neck, armpits and groins (Pastia's lines); the vesicles of chicken pox seem to follow the hollows of the body (they are more prominent along the depression of the spine on the back and in the hollows of both shoulder blades); very few rashes affect the palms of the hands and soles of the feet (secondary syphilis, rickettsia or spotted fevers, guttate psoriasis, hand, foot and mouth disease, keratoderma blennorrhagicum);
• Symmetry: e.g., herpes zoster usually only affects one side of the body and does not cross the midline.

A patch test may be ordered, for diagnostic purposes.

Treatment

Treatment differs according to which rash a patient has been diagnosed with. Common rashes can be easily remedied using steroid topical creams (such as hydrocortisone) or non-steroidal treatments. Many of the medications are available over the counter in the United States.

The problem with steroid topical creams i.e. hydrocortisone; is their inability to penetrate the skin through absorption and therefore not be effective in clearing up the affected area, thus rendering the hydrocortisone almost completely ineffective in all except the most mild of cases.

References

References

1. (2017). "Eszopiclone". F.A. Davis.
2. "Zolpidem". F.A. Davis.
3. Fisher, Alexander A.. (2008). "Fisher's Contact Dermatitis". PMPH-Usa.
4. "Lyme disease rashes and look-alikes". Centers for Disease Control and Prevention.
5. "Lyme disease: erythema migrans". National Institute for Health and Care Excellence.
6. (June 2012). "Diagnosis and management of Lyme disease". American Family Physician.
7. (May 2014). "Clinical practice. Lyme disease". The New England Journal of Medicine.
8. (2021-08-29). "A febrile illness with generalized papular rash involving the palms and soles". Clinical Infectious Diseases.
9. Rebecca B. Campen M.D.. (12 November 2009). "The Comprehensive Guide to Skin Care: From Acne to Wrinkles, What to Do (And Not Do) to Stay Healthy and Look Your Best". Abc-Clio.
10. "Hydrocortisone Topical".
11. "Hydrocortisone for mild inflammatory skin conditions".