A scaly patch on the outer elbow with a sharp border and silvery or gray scale points more toward psoriasis. A dry, intensely itchy patch in the inner elbow crease with blurry edges points more toward eczema. Where a rash appears is one of the most useful clues dermatologists use, but it isn't a diagnosis on its own, so a patch that won't settle down is worth having examined.
Here is how the two conditions tend to show up on different parts of the body, based on guidance from the American Academy of Dermatology (AAD) and other mainstream medical sources.
Inner elbows and knees vs outer elbows and knees
This is the classic dividing line between eczema and psoriasis.
- Inner elbows and backs of the knees, where the skin bends, are typical spots for eczema in older children and adults. The skin looks dry and rough, itches a lot, and may thicken or darken from scratching.
- Outer elbows and fronts of the knees are typical spots for plaque psoriasis. Plaques are raised and thick, with a clear edge and a buildup of silvery-white scale on lighter skin, or gray scale on darker skin. They may itch, but they can also burn or feel sore.
Two exceptions are worth knowing. In babies, eczema often starts on the cheeks, forehead and scalp. And the AAD notes that in children with darker skin, eczema often shows up on the fronts of the knees and elbows, so the "inside vs outside" rule is less reliable.
Scalp: flaking, plaques and where they stop
Flaking on the scalp has several possible causes.
- Scalp psoriasis forms thick, well-defined plaques with heavy scale. A helpful clue is where it stops: psoriasis often creeps just past the hairline onto the forehead, the back of the neck or around the ears.
- Seborrheic dermatitis, the cause of dandruff in adults and cradle cap in babies, tends to cause greasy, yellowish or white flakes, often with redness along the hairline, eyebrows and sides of the nose.
- Eczema can affect the scalp too, especially in infants. It usually causes dry, itchy patches with less defined edges.
Scalp psoriasis and seborrheic dermatitis can look very similar, and some people have features of both. Both are often treated with medicated shampoos or scalp products, but the right choice depends on the diagnosis.
Hands and feet: cracking, blisters and thick scale
The hands are one of the hardest places to tell the two apart.
- Hand eczema is common in adults. It is often triggered or worsened by frequent handwashing, wet work, cleaning products and other irritants. It can cause dryness, redness, painful cracks and tiny itchy blisters along the sides of the fingers and on the palms.
- Psoriasis on the palms and soles usually forms thick, well-defined, scaly patches that can crack painfully. A less common form, pustular psoriasis, causes small pus-filled bumps on the hands and feet. These bumps are not caused by an infection, and they are not contagious.
As a rough guide, tiny blisters lean toward eczema, and thick, sharply bordered scale leans toward psoriasis. Many hand rashes fall somewhere in between, though. A fungal infection on the feet or hands can also look similar, which is another reason to have a hand or foot rash examined before trying treatments on your own.
Face, eyelids and skin folds
- Face and eyelids: Eczema is common here. Eyelid skin is thin, so it reacts easily to cosmetics, skin care products and other things that touch it. Adults with eczema may notice thickened, darker skin around the eyes. Psoriasis on the face is less common. When it does appear, it is often along the hairline, on the eyebrows, or on the skin between the nose and upper lip.
- Skin folds: Psoriasis in the armpits, groin, under the breasts or in the crease of the buttocks is called inverse psoriasis. Because these areas stay moist, it usually looks smooth, shiny and red or discolored, with little or no scale, and it can feel sore. Eczema can also appear in folds, and so can yeast and fungal infections, which can look much alike.
Facial and fold skin is thinner and more sensitive than skin elsewhere. Many creams that are fine on the elbows are too strong for these areas, so check with a dermatologist before using a medicated cream on your face, eyelids, groin or underarms.
Nails: pitting and other changes worth mentioning
Nails can offer an important clue, so mention any changes at your visit, even if your main concern is a patch of skin.
- Psoriasis often affects the nails. The AAD lists tiny dents called pits, white, yellow or brown discoloration, crumbling, nails lifting away from the nail bed, and buildup of skin under the nail as signs of nail psoriasis.
- Eczema on the fingers near the nails can also change the nail surface, causing ridges or a wavy look. Pitting and nail lifting are more strongly linked with psoriasis.
Nail fungus can cause thickening and discoloration that looks like nail psoriasis, and the treatments are very different. If nail changes come with joint pain, swelling or morning stiffness, tell your dermatologist, since psoriasis is linked to a form of arthritis called psoriatic arthritis.
When a patch should be checked by a dermatologist
Location gives useful hints, but it can't confirm a diagnosis. See a dermatologist if:
- A patch hasn't improved with gentle, fragrance-free skin care and over-the-counter products
- The itch is disrupting your sleep or work
- The patch is thick, cracked, painful or spreading
- You notice nail changes, or joint pain, swelling or stiffness
- The rash oozes, forms yellow crusts or comes with a fever, which can signal an infection that needs prompt care
- It's on your face, eyelids, genitals or skin folds, where many over-the-counter products are too harsh or not recommended
At a first visit, a dermatologist will look closely at the patch, check other telltale spots like the scalp, nails and skin folds, and ask about itch, triggers and family history. Sometimes a small skin sample is needed to confirm the diagnosis. You can read more about what to expect at your first visit.
Bay Ridge Dermatology treats eczema, psoriasis, and hair and nail disorders for patients of all ages as part of our medical dermatology care. Once the diagnosis is clear, treatment can be matched to the condition and to the part of the body involved. Individual results vary.
If you have a patch that keeps coming back, we're happy to take a look. You can book online or call (347) 497-4984.
This article is general information, not medical advice. For advice about your own skin, see a dermatologist.