Diabetes-related foot ulcers are usually explained in terms of neuropathy, deformity and impaired perfusion. Yet almost every ulcer begins at the skin surface, and two of the most visible findings on a routine foot examination — dry, scaling skin (xerosis) and plantar callus (hyperkeratosis) — are among the earliest signals that the skin envelope is failing. Both are modifiable, both are assessable without specialised equipment, and both have been studied as predictors of ulceration.
Why Foot Skin Becomes Dry in Diabetes
Xerosis in the diabetic foot is not simply cosmetic or a consequence of ageing. Distal symmetrical polyneuropathy damages the small autonomic C-fibres supplying eccrine sweat glands. As sudomotor function declines, the stratum corneum loses water-binding capacity, and the skin becomes scaly, inelastic and prone to fissuring — most often at the heel margin, where mechanical stress is highest.
This link is measurable. Sheshah and colleagues assessed electrochemical skin conductance of the feet in 296 patients with diabetes and found that conductance fell progressively as neuropathy symptom and disability scores rose. Sudomotor failure tracks the same nerve damage that removes protective sensation, which is why dry skin and insensate skin so often appear together. The clinical consequence is a heel fissure in a foot that may not feel it, may not see it, and may have impaired perfusion and impaired immune response to any organism entering through it.
Dry Skin Predicts Ulceration
The most direct evidence comes from a prospective multicentre study by Panagoulias and colleagues, who followed 308 people with diabetes and no history of ulceration or critical limb ischaemia for six years. Foot skin dryness was assessed with a visual indicator plaster method, a simple colorimetric test of sweat production. Fifty-five participants developed a foot ulcer, an annual incidence of 2.97%. After adjustment for age, sex and diabetes duration, an abnormal indicator test was independently associated with ulceration (hazard ratio 3.32, 95% CI 1.46–7.55).
The performance profile is informative: the skin dryness test was highly sensitive (0.86) but non-specific (0.49), whereas a high neuropathy disability score or elevated vibration perception threshold showed the opposite pattern. Assessing the skin therefore complements, rather than replaces, conventional neurological screening.
Callus: A Visible Record of Excess Pressure
Callus forms where repetitive shear and vertical load exceed tissue tolerance. In the insensate foot it becomes a rigid foreign body that further raises local pressure, and haemorrhage within callus is a recognised pre-ulcerative lesion.
A meta-analysis by Guo and colleagues pooling 20 studies and 4,238 patients identified callus as a significant risk factor for ulcer recurrence (OR 5.70, 95% CI 1.36–23.89), alongside peripheral neuropathy (OR 4.05), peripheral vascular disease (OR 3.94) and previous ulceration (OR 4.10). In a prospective cohort of 2,432 patients used to build a risk-prediction nomogram, Lv and colleagues reported a foot ulcer incidence of 12.4% and found callus to be one of five independent predictors (OR 2.92, 95% CI 2.13–4.00), together with abnormal foot skin colour, diminished pedal pulses, body mass index and prior ulceration.
Removing callus does more than improve appearance. In a systematic review of interventions targeting modifiable ulcer risk factors, van Netten and colleagues concluded that callus removal reduces peak plantar pressure, and that custom-made therapeutic footwear both lowers plantar pressure and may reduce callus formation. Debridement is a sharp-instrument procedure for trained clinicians; over-the-counter salicylic acid preparations and self-paring in a neuropathic or ischaemic foot risk iatrogenic wounds.
What Emollients Can and Cannot Do
Topical treatment of xerosis is widely recommended but unevenly evidenced. A systematic review by Parker and colleagues identified 22 experimental studies covering 12 active ingredients; urea was by far the most studied (14 studies), followed by ammonium lactate. Methodological quality was poor to moderate and outcome measures were inconsistent, so the authors could not recommend any single agent over another.
More recent work suggests the formulation may matter less than consistent use. In a randomised, double-blind comparison of two 10% urea creams in patients with diabetic foot syndrome, Tejeda Ramírez and colleagues found improved skin quality in 95% of feet irrespective of which product was applied, with reductions in xerosis, hyperkeratosis and pre-ulcerative signs such as subkeratotic bruising; cost did not predict benefit. The sample was small (10 patients, 20 feet), but it supports the practical message that an inexpensive urea-based emollient used daily is reasonable. Standard foot-care guidance remains to avoid applying emollient between the toes, where retained moisture promotes maceration.
Where Skin Care Sits in Prevention Frameworks
The 2023 International Working Group on the Diabetic Foot guideline on prevention places these findings in context. It recommends screening for loss of protective sensation and peripheral artery disease, education on foot self-care, treatment of any pre-ulcerative lesion — a category that includes callus, blisters, fissures and haemorrhage into callus — therapeutic footwear with a demonstrated pressure-relieving effect, and integrated foot care for people at moderate-to-high risk.
Clinical Summary
Xerosis and callus are not incidental findings in the diabetic foot. Dry skin reflects autonomic nerve damage and independently predicts ulceration with high sensitivity, making it a useful complement to sensory testing. Callus marks the region of highest mechanical load and is associated with a several-fold increase in ulcer risk; professional debridement measurably reduces peak plantar pressure. Emollient evidence is limited in quality, but urea-based preparations are the most studied and appear effective regardless of price. Current international guidance treats skin inspection, emollient use and treatment of pre-ulcerative lesions as core components of ulcer prevention rather than optional adjuncts.
References
- Panagoulias GS, Eleftheriadou I, Papanas N, et al. Dryness of foot skin assessed by the visual indicator test and risk of diabetic foot ulceration: a prospective observational study. Frontiers in Endocrinology. 2020;11:625.
- Sheshah E, Madanat A, Al-Greesheh F, et al. Electrochemical skin conductance to detect sudomotor dysfunction, peripheral neuropathy and the risk of foot ulceration among Saudi patients with diabetes mellitus. Journal of Diabetes and Metabolic Disorders. 2016;15:29.
- Guo Q, Ying G, Jing O, et al. Influencing factors for the recurrence of diabetic foot ulcers: a meta-analysis. International Wound Journal. 2023;20(5):1762–1775.
- Lv J, Li R, Yuan L, et al. Development and validation of a risk prediction model for foot ulcers in diabetic patients. Journal of Diabetes Research. 2023;2023:1199885.
- van Netten JJ, Sacco ICN, Lavery LA, et al. Treatment of modifiable risk factors for foot ulceration in persons with diabetes: a systematic review. Diabetes/Metabolism Research and Reviews. 2020;36(Suppl 1):e3271.
- Parker J, Scharfbillig R, Jones S. Moisturisers for the treatment of foot xerosis: a systematic review. Journal of Foot and Ankle Research. 2017;10:9.
- Tejeda Ramírez S, Tardáguila-García A, López-Moral M, et al. Randomized double-blind cost-effectiveness comparison of two 10% urea creams in patients with diabetic foot syndrome. Advances in Skin & Wound Care. 2024;37(5):1–7.
- Bus SA, Sacco ICN, Monteiro-Soares M, et al. Guidelines on the prevention of foot ulcers in persons with diabetes (IWGDF 2023 update). Diabetes/Metabolism Research and Reviews. 2024;40(3):e3651.
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