We all know the message: slip, slop, slap, seek, and slide. Sun safety has been the cornerstone of Australian skin-cancer prevention for decades. And rightly so — the majority of skin cancers we see in clinics are directly linked to ultraviolet (UV) radiation.

But what’s less understood is that not every skin cancer starts with sunlight. Some develop in places that rarely see the sun at all — the soles of the feet, under nails, or even within old scars.

These are the non-UV-related skin cancers, and while they’re far less common, they deserve just as much awareness.

What Does “Non-UV-Related” Mean?

When we talk about non-UV skin cancers, we’re referring to those caused by factors other than chronic sun exposure. They might arise because of viral infections, a weakened immune system, chemical exposure, chronic wounds, radiation, or inherited genetic conditions.
 These cancers don’t follow the “sun-damaged skin” pattern we usually associate with fair complexions or outdoor workers — which means they can be missed or misdiagnosed for longer.

Viral Influences: More Than Just the Common Cold

Certain viruses are known to play a role in skin cancer formation.

• Human papillomavirus (HPV) can contribute to squamous cell carcinomas (SCCs), especially around the nails and genital skin.
  
  
• Merkel cell polyomavirus is associated with Merkel cell carcinoma (MCC) — a rare but aggressive cancer that often appears as a fast-growing, painless, reddish-purple lump. MCC tends to occur in older adults or those with compromised immunity.
  
  
• Human herpesvirus-8 (HHV-8) causes Kaposi sarcoma, a vascular tumour more common in people with weakened immune systems, such as organ-transplant recipients or individuals living with HIV.
  
  

Viruses interact with our DNA in complex ways, sometimes triggering cells to multiply uncontrollably. While most people infected with these viruses never develop cancer, immunity and early detection play major roles in prevention.

When the Immune System Is Weakened

Our immune system is our built-in surveillance network, identifying and eliminating abnormal cells before they become dangerous. When that system is suppressed — by medication, disease, or age — the skin becomes more vulnerable.

 Transplant recipients, for example, often require lifelong immunosuppressant medication to prevent organ rejection. These drugs, while lifesaving, increase the risk of developing multiple or aggressive SCCs and other unusual tumours.

 Even mild immune suppression (from long-term steroid use or poorly controlled chronic illness) can tip the balance. Regular professional skin checks are vital for these groups because changes can develop quickly and silently.

Chemicals, Radiation, and Scars

Long before “sun safety” was a public message, industrial workers faced another risk: arsenic exposure. Once used in pesticides, mining, and even early medicines, arsenic can lead to multiple small cancers on palms, soles, and torso decades after exposure.

Likewise, ionising radiation — such as previous radiotherapy or repeated X-rays — can cause later-onset skin cancers, often aggressive and arising in previously treated sites.

And then there are Marjolin ulcers — skin cancers that develop in old burn scars or chronic wounds. They can take years, even decades, to appear and tend to be invasive once they do. Any long-standing ulcer or non-healing scar should always be reviewed by a clinician.

Genetic Conditions and Family Syndromes

Some people are born with DNA changes that make their skin more prone to cancer, even without UV damage.

• Basal Cell Naevus (Gorlin) Syndrome leads to multiple early-onset basal cell carcinomas.
• Xeroderma Pigmentosum (XP) affects DNA repair, so even minor everyday exposures can cause mutations.
• Muir-Torre Syndrome links internal organ cancers with sebaceous gland tumours on the skin.

While rare, these syndromes remind us that genetics and cell repair play just as big a role as sunshine in our skin health.

What to Watch For

Non-sun-related skin cancers can appear anywhere on the body — not just sun-exposed areas. Warning signs include:

• New lumps, nodules, or plaques that grow quickly
• Ulcers or sores that fail to heal
• Discolouration, thickening, or bleeding in scars or radiation sites
• Changes beneath nails or on the soles of the feet
• Any new or persistent spot that looks or feels different from the rest
  
  

Awareness Is Prevention

In Western Australia, we’re fortunate to have strong awareness around sun protection — but skin cancer prevention doesn’t end when the hat goes on.
 Regular, head-to-toe skin checks are essential, especially for anyone with immune suppression, a history of radiation or chronic wounds, or exposure to chemicals through past work.
 If you notice anything unusual, don’t wait for it to “settle down.” Early review can make all the difference.

At Skin ChX, we’ve seen first-hand that non-UV skin cancers can surprise even the most sun-safe people. The goal isn’t fear — it’s awareness. Because the more we understand about the many pathways to skin cancer, the better we can prevent, detect, and treat them early.