Dermatitis develops when your skin’s protective barrier is compromised, whether by genetics, direct contact with an irritating substance, or an underlying condition like poor circulation. There isn’t one single cause. Dermatitis is actually an umbrella term for several types of skin inflammation, and each type has its own set of triggers. Nearly 10% of people aged 16 and older have atopic dermatitis (eczema) alone, making it one of the most common skin conditions worldwide.
Atopic Dermatitis: Genetics and Immune Overreaction
Atopic dermatitis, commonly called eczema, is the type most people think of. It starts with a problem in the skin barrier itself. Your outermost layer of skin depends on a protein called filaggrin to stay strong, flexible, and hydrated. Some people carry genetic mutations that reduce filaggrin production, leaving skin that lets moisture escape too easily and allows irritants and allergens to slip through. These mutations appear across all ethnic groups, with roughly 5% of the population carrying them.
When the barrier is weakened, skin cells detect the incoming threats and release signaling molecules that activate your immune system. The immune response is disproportionate, producing a flood of inflammatory chemicals that cause the redness, swelling, and intense itch characteristic of eczema. This inflammation further weakens the skin barrier, which lets in more irritants, which triggers more inflammation. It’s a self-reinforcing cycle. The same inflammatory signals also suppress the skin’s natural antimicrobial defenses, which is why people with eczema are especially prone to bacterial skin infections.
You don’t need a filaggrin mutation to develop atopic dermatitis. A family history of eczema, asthma, or hay fever significantly raises your risk, and environmental factors play a major role in whether the condition actually shows up and how often it flares.
Contact Dermatitis: Irritants and Allergens
Contact dermatitis happens when something touches your skin and causes a reaction. It comes in two forms, and the distinction matters because they work differently.
Irritant contact dermatitis is the more common type. It doesn’t involve an immune reaction. The substance directly damages your skin cells. Common irritants include soaps and detergents, antiseptics, solvents, machine oils, cement, acids, and even water (particularly hard or heavily chlorinated water). Frequent handwashing alone can strip enough natural oils from your skin to cause it. The reaction can happen to anyone if the exposure is strong enough or repeated often enough.
Allergic contact dermatitis is an immune-mediated reaction to a specific substance your body has become sensitized to. Common allergens include:
- Nickel and cobalt in jewelry, belt buckles, and watch backs
- Fragrances and preservatives in cosmetics, lotions, and toiletries
- Hair dye and nail varnish hardeners
- Latex and rubber chemicals
- Epoxy resin adhesives
- Textile dyes and resins
- Certain plants like chrysanthemums, daffodils, tulips, and primula
The tricky part is that allergic contact dermatitis requires a sensitization period. You might use a product for weeks, months, or even years before your immune system suddenly decides to react to it. Once sensitized, even tiny amounts of the allergen trigger a rash, typically appearing 12 to 72 hours after contact.
Seborrheic Dermatitis: Yeast on the Skin
Seborrheic dermatitis shows up as flaky, scaly patches on oily areas of the body, particularly the scalp, face, and chest. Dandruff is a mild form of it. This type is closely linked to a yeast called Malassezia that lives naturally on everyone’s skin. In some people, the yeast triggers an inflammatory response that leads to redness and flaking. Certain Malassezia species are found in higher concentrations on affected skin, though researchers still don’t fully understand why some people react to a fungus that coexists peacefully with most.
Seborrheic dermatitis tends to worsen during periods of stress, illness, or cold, dry weather. It’s more common in people with weakened immune systems and in those with neurological conditions like Parkinson’s disease.
Stasis Dermatitis: Poor Circulation in the Legs
Stasis dermatitis develops in the lower legs when veins can’t efficiently return blood to the heart. Veins contain one-way valves that keep blood moving upward against gravity. As you age, those valves can weaken and the veins stretch, allowing blood to pool in the legs instead of circulating back. The pooled blood and fluid leak from the veins and put pressure on the surrounding skin from the inside.
That pressure causes swelling, redness, itching, and a heavy or achy feeling. Over time, the skin can darken, thicken, and become leathery. Left untreated, stasis dermatitis can progress to open sores that are slow to heal. It’s most common in older adults and people with a history of blood clots, varicose veins, or prolonged periods of standing.
Occupational Exposure
Your job can put you at significantly higher risk. Occupational contact dermatitis is one of the most reported work-related skin conditions, and certain industries carry consistently elevated rates. Hairdressers are exposed to nickel, acrylates, and formaldehyde-based products. Cement workers encounter chromium and nickel. Medical and dental workers handle formaldehyde, glutaraldehyde, and latex. Mechanics, printers, machinists, and electronics workers regularly contact epoxy resins, rubber chemicals, and solvents.
Less obvious high-risk jobs include bakers (exposed to peroxides and cinnamon compounds), florists (plant-based sensitizers in tulips and chrysanthemums), and farm workers (pesticides, fungicides, and poison ivy). Even housekeeping work carries risk from repeated exposure to cleaning chemicals, nickel, and formaldehyde-containing products. In many of these jobs, the combination of frequent wet work and chemical exposure creates conditions for both irritant and allergic dermatitis simultaneously.
Environmental and Stress Triggers
If you already have dermatitis, external conditions play a major role in when and how badly it flares. Low humidity and cold air dry out the skin, while high heat encourages the growth of microorganisms that worsen skin conditions. Airborne particles from wildfires, industrial pollution, and dust storms can settle on the skin and aggravate both allergic and irritant dermatitis. Floodwaters, increasingly common in extreme weather events, can inflame skin and trigger contact reactions.
Psychological stress is one of the most underestimated triggers. Stress both causes and worsens dermatitis through measurable changes in immune function and skin barrier integrity. It’s not that dermatitis is “in your head,” but rather that stress hormones shift your immune system toward the same type of inflammatory response that drives eczema flares. Many people notice their worst outbreaks during periods of high anxiety, poor sleep, or major life changes, and that pattern has a real biological basis.
Why Some People Get It and Others Don’t
Dermatitis results from an interaction between your genetic makeup, the state of your skin barrier, and what your skin encounters day to day. Two people can use the same soap or wear the same nickel earrings and have completely different outcomes. The person whose skin barrier is already compromised, whether from inherited filaggrin mutations, dry winter air, or frequent handwashing, is the one more likely to develop a reaction.
Age also shifts the equation. Children are more prone to atopic dermatitis, with many outgrowing it by adolescence. Adults more commonly develop contact dermatitis as occupational and product exposures accumulate over years. Stasis dermatitis is largely a condition of aging circulatory systems. At any point, stress, climate, and daily habits can tip the balance from clear skin to an active flare.