Skin Allergy
Evaluation and management of allergic skin reactions and recurrent rashes
What is skin allergy?
A skin allergy is the immune system reacting to a substance that is harmless to most people. It happens on two different clocks, and telling them apart is most of the work.
An immediate reaction appears within minutes to a couple of hours of contact or of eating something, produces raised weals that move around the body and fade within a day, and is driven by histamine released from cells in the skin. A delayed reaction appears one to three days after the skin touches something, sits exactly where the contact was, and is driven by immune cells that have learnt to recognise that substance.
The delayed kind builds with exposure, so a metal, a dye, a fragrance, a cosmetic or a rubber compound you have used for years can start causing trouble. The immediate kind is often set off by an infection, a medicine or a food, and in many people no cause is ever identified.
What you might notice
- A rash that keeps coming back
- Itchy dry patches of skin
How it is diagnosed
Your doctor works mostly from where the rash is and when it appears, so the history carries the diagnosis. The distribution is the clue: earlobes and the navel point to metal, the scalp margin and neck to hair dye, the feet to footwear, the eyelids to something transferred by your hands, and the hands themselves to work.
They will ask what is new in the last few weeks, what you put on your skin, what your job involves, what medicines and supplements you take, and whether the rash comes and goes within hours or stays put for days.
They will also examine you for swelling of the lips, the tongue or the eyelids, and ask about breathlessness or faintness with an episode, since those change the urgency completely. Where a contact cause is suspected, your doctor can arrange testing to identify the substance.
Recovery
An immediate reaction settles within hours to a day once it is treated, though new weals can keep appearing for a few days after a single trigger. Most short-lived episodes are over within two to six weeks.
Contact reactions clear over two to three weeks once the substance is out of your life, and they return in days if it comes back. Skin on the hands recovers more slowly, sometimes six weeks, because it stays in use.
Long-standing hives are the slow one. They are controlled with daily medication instead of cured, and most settle on their own over months to a few years, so your doctor will keep you comfortable and review the dose periodically. There is no time off work, though daytime drowsiness with older antihistamines is worth mentioning if you drive or operate machinery.
If it is left untreated
A mild reaction to something you have already identified and removed needs nothing beyond avoiding it.
Left alone, contact reactions keep recurring with each exposure, and repeated inflammation thickens and cracks the skin, which takes far longer to heal than the original rash. Skin broken by scratching becomes infected. Untreated hives disturb sleep, and severe itching over months affects work and mood.
There is one situation that is genuinely dangerous and needs no waiting. Swelling of the lips, the tongue or the throat, a tight chest, difficulty breathing, dizziness or faintness after an exposure is a severe allergic reaction and needs emergency care immediately. If that has ever happened to you, your doctor should identify the trigger and tell you what to carry and what to do.
Questions about skin allergy
How do I find out what I am allergic to?
Where the rash sits and when it appears does most of the identifying, so your doctor will take a detailed history of what is new in your cosmetics, jewellery, footwear, work and medicines. Where a contact cause is suspected, testing places small amounts of common triggers on your back under tape for two days, with readings at two and four days, and it identifies the substance reliably. Immediate reactions are a different question and use different tests. Bring the actual products and a photograph of the rash at its worst to the appointment.
Will antihistamines have to be taken forever?
For most people no. A short-lived bout of hives settles within weeks, and the medication stops with it. Long-standing hives are different: they are controlled day to day with a regular non-drowsy antihistamine, and your doctor may increase the dose above the standard one, which is a recognised approach and safer than adding drowsy tablets. Most long-standing cases settle on their own over months to a few years, and treatment is stepped down as they do. Taking the tablet every day works better than waiting for weals and treating them.
When is a reaction an emergency?
Go to a hospital immediately, without waiting to see if it improves, for swelling of the lips, tongue, throat or the sound of the voice, difficulty breathing or a tight chest, a sudden widespread rash with dizziness, vomiting or faintness, or any reaction that comes on within minutes of a medicine, an injection or a food. These can worsen very quickly. A rash alone, with no swelling and no breathing difficulty, can be dealt with in clinic. If you have ever had a severe reaction, ask your doctor what to carry and how to use it.
Other dermatology & cosmetology treatments
Treatment of acne and acne-related marks based on skin type, severity and recurrence
Day CareEvaluation and treatment of uneven skin tone, dark spots and other pigmentation concerns
Day CareTalk to a care coordinator about skin allergy
Leave a number and a care coordinator calls you back with what the treatment involves and which hospital it would be at. They book a consult only if you want one