The standardized prevalence (males and females combined) of seborrheic keratoses (SKs) by age (with 95% confidence intervals) (linear trend χ21=4.37, P=.04).
Body map showing the distribution of seborrheic keratoses recorded.
Gill D, Dorevitch A, Marks R. The Prevalence of Seborrheic Keratoses in People Aged 15 to 30 YearsIs the Term Senile Keratosis Redundant?. Arch Dermatol. 2000;136(6):759-762. doi:10.1001/archderm.136.6.759
DamianoAbeniMD, MPHMichaelBigbyMDPaoloPasquiniMD, MPHMoysesSzkloMD, MPH, DrPHHywelWilliamsPhD, FRCP
Seborrheic keratoses (SKs) are common skin lesions that have been shown to occur with increasing age, although the age of onset is not well recorded.
To determine the prevalence, nature, and distribution of SKs in young people.
One hundred seventy people aged 15 to 30 years were given a total body examination during which the presence, number, site, and size of SKs were recorded. Biopsy specimens were taken from the first 22 people who had lesions clinically diagnosed as SKs. Data on age, skin type, eye color, and hair color were recorded for all respondents.
Forty (23.5%) of 170 respondents had at least one SK, with no significant difference between the sexes. There was an increase in prevalence with age from 15.7% in 15- to 19-year-olds to 32.3% in those aged 25 to 30 years. The size of the SKs also increased with age. A total of 77.5% of SKs were found on the trunk and 22.5% on the limbs, head, and neck. There was no correlation between SKs and any particular hair and eye color or skin type.
These findings confirm that SKs are common lesions in young Australians, appearing in a substantial proportion of people younger than 30 years. The term senile keratosis is no longer appropriate for these lesions.
SEBORRHEIC KERATOSES (SKs) (also known as seborrheic warts, basal cell papillomas, senile keratoses) are very common skin lesions. As some of the descriptive names imply, they have been considered to be tumors of the elderly. Despite the recent advances in our understanding of many other less common skin diseases, little is reported about the true epidemiology of these lesions and even less is reported about their etiology. Data on their prevalence have been based on clinical diagnosis alone.
It has been said that SKs usually appear in the fifth decade of life in people living in temperate climates but may develop earlier in tropical regions.1,2 A study3 of a British population found that SKs were present in people younger than 40 years (males, 8.3%; females, 16.7%), whereas SKs were reported to be absent in a prevalence survey on skin diseases in Kenya.4
A recent study5 in Australia that examined all age groups in a hospital population reported a 12% prevalence for SKs in those aged 15 to 25 years. This was an unexpected finding, given the common view that these skin lesions are found in people mainly older than 50 years who live in temperate climates. However, the number of participants in the 15- to 25-year age group in the recent Australian report was small.
The aim of our study was to determine more accurately the prevalence of SKs in people younger than 30 years. Histological confirmation of the clinical diagnosis was also undertaken to ensure accuracy of the data being gathered.
Following approval from the Human Research and Ethics Committee, St Vincent's Hospital, Melbourne, Australia, persons aged 15 to 30 years in 2 separate general practices had the study explained to them and were asked if they would like to have a full body skin examination. These people had made appointments for reasons unrelated to the possibility of an SK. The respondents filled out a consent form advising them that a shave biopsy may be performed to confirm the diagnosis if a lesion resembling an SK was found. Data on date of birth, skin type (always burns, burns first then tans/sometimes tans, always tans), hair color, and eye color were recorded at the time of the examination. A full body examination (excluding the underpants area in both sexes and breasts in females) was performed. The number, size (greater or less than 3 mm), color (skin colored, yellow, light and dark brown), and site of SKs were recorded.
Clinical diagnostic criteria for early lesions included discrete, round, or oval skin-colored papules with distinct keratotic and follicular plugging, stuck-on appearance, and colors ranging from skin-colored to heavily pigmented. A fine granular loss of reflective quality over the surface of the lesion compared with a shiny surface on stretching the surrounding skin was also used to detect early lesions.1,6
An incident light source (magnifying lens with a built-in globe) was used to detect elevated skin lesions and also examine surface texture of individual skin lesions (in particular, the loss of reflective quality of skin found over SKs).
The first 22 respondents diagnosed as having an SK clinically had a shave biopsy specimen taken without local anesthetic. The biopsy specimens, approximately 1 to 3 mm in diameter, were placed in 10% formalin and, wax embedded, stained with hematoxylin-eosin, and reported on by a single dermatopathologist (A.D.).
Sample size calculation was made on a predicted minimum prevalence of 12% found in the previous Australian study.5 χ2 Analyses for general associations and for linear trend were used. Odds ratios and 95% confidence intervals for suspected predictor variables for SKs were determined by logistic regression analysis. The Australian population was used as the reference population for standardization and calculation of confidence intervals. Statistical calculations were performed using the Intercooled Stata 5 statistics program.7
One hundred seventy people were examined, of whom 82 (48.2%) were male and 88 (51.8%) were female. They were all Caucasian and included Anglo-Saxon, Mediterranean (Greek and Italian), and Sri Lankan (n=1) subjects.
Histological testing on 20 (91%) of the 22 shave biopsy specimens confirmed the clinical diagnosis of SK. Of the other 2, one was reported as a compound melanocytic nevus, and in one there was insufficient material for a histological diagnosis. Given the high correlation between the clinical diagnosis and histological confirmation, the 19 subsequent study participants with SKs were diagnosed on clinical grounds alone.
Forty (23.5%) of the 170 subjects examined were found to have at least one SK, with the total number of lesions being 80. Subjects were grouped into 3 age categories: 15 to 19 years, 20 to 24 years, and 25 to 30 years. There was an increasing standardized prevalence of SKs with increasing age, ranging from 15.7% (15-19 years) to 32.3% (25-30 years) (linear trend χ21=4.37, P=.04) (Figure 1). The overall prevalence for females was 26.1% compared with 20.7% for males, with no significant difference with age between the sexes (Table 1).
Most participants (62.5%) who were found to have SKs had only one, with the proportion having more than one lesion varying with age (Table 2). The size of SKs increased with age, with younger people having a higher proportion less than 3 mm and a lower proportion greater than 3 mm than the older people (linear trend χ22=3.76, P=.05).
Most SKs (77.5%) were found on the trunk compared with the limbs and head (22.5%) (Figure 2). When considering individuals, 67.5% had SKs on the trunk alone, 25.0% had them on the limbs and trunk, 5.0% had them on the limbs alone, and 2.5% (1 person) had a single lesion on the forehead. Only 3 SKs were present on the lower limbs.
There was an association between the frequency of SKs and body site, with more appearing on the trunk compared with the limbs and head and neck with increasing age (linear χ22=4.12, P=.04). There was no association between color of SKs and increasing age (linear χ22=1.14, P=.24).
A logistic regression analysis revealed increasing age to be the only variable significantly associated with the presence of SKs (Table 3). There was a 62% chance of having an SK with each 5 years of advancing age. Skin type, hair color, and eye color were not independent predictor variables for SKs.
This study illustrates that SKs are common in Australians aged 15 to 30 years. The first question to ask is whether the lesions recorded really were SKs. The high correlation between clinical diagnosis and histopathological findings suggests that most were.
The next question is whether those included in the sample are a true reflection of the Australian community in this age group. In this study, patients were approached consecutively in general practice, and, therefore, it was not a truly randomized sample. If patients with skin lesions were more likely to participate in the study because they had, or were concerned about, particular skin lesions, it could give a falsely high prevalence. However, respondents were attending for reasons unrelated to skin tumors, and even among people with SKs, most were not aware that the lesions were present. Those few who were aware of their presence were not concerned about the lesions and were certainly not seeking treatment for them. This reduces the likelihood that positive selection bias has affected the study results.
The distribution of SKs was predominantly truncal in our population, with more than 3 of 4 found on the trunk, which accounts for only 36% of body surface area using the rule of nines.8 In addition, SKs have been reported to occur anywhere on the body except the palms and soles but most commonly on the midline of the back and chest and then on the temple, scalp, and sides of the neck.9
The possible association between sun exposure and SKs has been raised in the past.5,10 However, the data reported herein do not support an increased frequency of the lesions in the traditionally heavily light-exposed areas. Several possibilities exist to explain this. First, it may be that some SKs are associated with very heavy sunlight exposure over the years. Thus, they will not predominate until later decades in the exposed areas of the body, such as the head and neck or dorsum of the hands.
The second possibility is that changing behavior in young people compared with older people, where the truncal exposure is almost as great now as the traditional light-exposed areas, means that the distribution reported herein is a reflection of changing sunlight exposure patterns of the younger community. Finally, of course, there is the possibility that sunlight has no role at all in the development of SKs.
Nevertheless, SKs are common in young people. Little is known about their origin, and more work is required, particularly in young people when the SKs are first appearing, to determine what causes them. In the meantime, our data suggest that the term senile keratosis is no longer appropriate.
Accepted for publication December 10, 1999.
This work was supported with an internal research grant of the Department of Dermatology, St Vincent's Hospital, Melbourne, Victoria, Australia.
We thank the medical practices that allowed recruitment of their patients and the patients themselves for participating. Damien Jolley, MSc(Stats), helped with statistical advice.
A cooperative effort of the Clinical Epidemiology Unit of the Istituto Dermopatico dell'Immacolata-Istituto di Ricovero e Cura a Carattere Scientifico (IDI-IRCCS) and the Archives of Dermatology
Corresponding author: Robin Marks, MBBS, MPH, The University of Melbourne, Department of Medicine (Dermatology), St Vincent's Hospital, Melbourne, 41 Victoria Parade, Fitzroy, Victoria 3065, Australia.
This point prevalence study indicates that seborrheic keratoses occur in young patients and that their number increases with age. Please see: Glanz SA. How to Test for Trends in Primer of Biostatistics. 3rd ed. New York, NY: McGraw-Hill Inc; 1992:218-277, for an understandable discussion of statistical testing for trends, and the article by Bigby titled "Odds Ratios and Relative Risks" in this issue of the ARCHIVES (page 770) for a brief explanation of odds ratios.—Michael Bigby, MD, Editor