For basic forms of contact dermatitis, your doctor will be able to prescribe you a strong corticosteroid that you can apply several times a day, and you should see symptoms reduce within 24-48 hours. More complex forms of skin problems should be referred to a dermatologist.
Or, of course, you could just avoid questionable fabrics altogether.
Personally, I find woollen products blended with any kind of synthetic to be problematic, whether they are jumpers, blankets, or scarves. Not only do they turn my neck itchy and red for several days, in the case of wool/poly-blend jumpers, I also end up sweating underneath because my skin can't breathe. I've alleviated this by avoiding all synthetic blended fabrics, and remain extremely cautious when buying any clothing to read the material composition on the tag.
According to the New Zealand Dermatological Society, the steps you should take to avoid textile contact dermatitis include wearing only natural fabrics (e.g. cotton, linen), wearing only light-coloured clothing (they have less dye), wearing loose clothing when it's warm or humid, and avoiding any items that say "non-iron", "dirt repellent", or "wash separately" on the tag, because these will either be chemically treated or contain dye that easily bleeds.
It's not just the fabrics themselves that can cause you to itch, chafe, sweat, or your skin to become inflamed. If you find yourself with mysterious skin irritation and suspect it's clothing-related, there are a couple of other things that could be harming you aside from the material itself.
Firstly, you might not be washing your new clothes prior to wearing them. Before the first wash, they contain the highest concentration of residual chemicals from the
manufacturing process, and may have also attracted dust and mites from the storage and shipping process. There's no legal obligation for clothing manufacturers to declare the chemicals used in production on tags, so there's no telling what you're being exposed to.
A change in your laundry's washing powder can also bring about skin irritation or allergic reactions. It's often the fragrance or other harsh chemical additives that make washing powder an irritant, so you may want to change back to a product you've used before without issues (or switch to a natural product). You can also wash your clothes with plain soap or shampoo that doesn't aggravate your skin.
Your skin reaction might be as simple as an allergy to the latex in the elastic in clothing, or even the zips, buttons, or studs when they're made out of nickel (a metal and common allergen).
Don't forget that it might not be your clothing causing you problems. Other material, such as bedding, mattresses, carpet, even furniture, can bring on contact dermatitis of some form. If you're having irritation problems and can't find the culprit, think about every material in your home that directly touches your skin. As contact dermatitis usually flares up almost instantly, it won't take too long to figure out what's to blame.
