Ichthyosis differs from simple dry skin (xeroderma Xeroderma Xeroderma is dry skin that is neither inherited nor associated with systemic abnormalities. Xeroderma results from delayed shedding of the superficial cells of the skin, yielding fine white... read more 
) by its association with a systemic disorder or drug, inheritability, severity, or a combination. Ichthyosis can also be much more severe than xeroderma.
Inherited ichthyoses
Inherited ichthyoses, which are characterized by excessive accumulation of scale on the skin surface, are classified according to clinical and genetic criteria ( see Table: Clinical and Genetic Features of Some Inherited Ichthyoses Clinical and Genetic Features of Some Inherited Ichthyoses 
). Some occur in isolation and are not part of a syndrome (eg, ichthyosis vulgaris, X-linked ichthyosis, lamellar ichthyosis, congenital ichthyosiform erythroderma [epidermolytic hyperkeratosis]). Other ichthyoses are part of a syndrome that involves multiple organs. For instance, Refsum disease Classic Refsum disease Peroxisomes are intracellular organelles that contain enzymes for beta-oxidation. These enzymes overlap in function with those in mitochondria, with the exception that mitochondria lack enzymes... read more and Sjögren-Larsson syndrome (hereditary intellectual disability and spastic paralysis caused by a defect in fatty aldehyde dehydrogenase) are autosomal recessive Autosomal Recessive Genetic disorders determined by a single gene (Mendelian disorders) are easiest to analyze and the most well understood. If expression of a trait requires only one copy of a gene (one allele)... read more conditions with skin and extracutaneous organ involvement.
A dermatologist should assist in diagnosis and management, and a medical geneticist should be consulted for genetic counseling.
Clinical and Genetic Features of Some Inherited Ichthyoses
Acquired ichthyosis
Ichthyosis may be an early manifestation of some systemic disorders (eg, leprosy Leprosy Leprosy is a chronic infection usually caused by the acid-fast bacilli Mycobacterium leprae or the closely related organism M. lepromatosis. These organisms have a unique tropism... read more 
[Hansen disease], hypothyroidism Hypothyroidism Hypothyroidism is thyroid hormone deficiency. Symptoms include cold intolerance, fatigue, and weight gain. Signs may include a typical facial appearance, hoarse slow speech, and dry skin. Diagnosis... read more 
, lymphoma Overview of Lymphoma Lymphomas are a heterogeneous group of tumors arising in the reticuloendothelial and lymphatic systems. The major types are Hodgkin lymphoma Non-Hodgkin lymphoma See table Comparison of Hodgkin... read more , AIDS Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection results from 1 of 2 similar retroviruses (HIV-1 and HIV-2) that destroy CD4+ lymphocytes and impair cell-mediated immunity, increasing risk of certain... read more 
, multiple myeloma Multiple Myeloma Multiple myeloma is a cancer of plasma cells that produce monoclonal immunoglobulin and invade and destroy adjacent bone tissue. Common manifestations include lytic lesions in bones causing... read more 
). Some drugs cause ichthyosis (eg, nicotinic acid, triparanol, butyrophenones). The dry scale may be fine and localized to the trunk and legs, or it may be thick and widespread.
Biopsy of ichthyotic skin is usually not diagnostic of the systemic disorder; however, there are exceptions, most notably sarcoidosis Sarcoidosis Sarcoidosis is an inflammatory disorder resulting in noncaseating granulomas in one or more organs and tissues; etiology is unknown. The lungs and lymphatic system are most often affected, but... read more 
, in which a thick scale may appear on the legs, and biopsy usually shows the typical granulomas.
Treatment of Ichthyosis
Minimization of exacerbating factors
Moisturization and keratolytics
Sometimes infection prophylaxis
When ichthyosis is caused by a systemic disorder, the underlying disorder must be treated for the ichthyosis to abate. Other treatments of ichthyosis include emollients and keratolytics and avoiding drying (1 Treatment reference Ichthyosis is scaling and flaking of skin ranging from mild but annoying dryness to severe disfiguring disease. Ichthyosis can also be a sign of systemic disease. Diagnosis is clinical. Treatment... read more 
).
Moisturization and keratolytics
In any ichthyosis, there is impaired epidermal barrier function, and moisturizers Moisturizing agents Topical dermatologic treatments are grouped according to their therapeutic functions and include Cleansing agents Moisturizing agents (emollients, skin hydrators, and softeners) Drying agents... read more should be applied immediately after bathing. Substances that are applied to the skin may have increased absorption. For example, hexachlorophene products should not be used because of increased absorption and toxicity.
An emollient, preferably plain petrolatum, mineral oil, or lotions containing urea or alpha-hydroxy acids (eg, lactic, glycolic, and pyruvic acids), should be applied twice daily, especially after bathing while the skin is still wet. Blotting with a towel removes excess applied material.
Ichthyosis typically responds well to the topical keratolytic propylene glycol. To remove scale (eg, if ichthyosis is severe), patients can apply a preparation containing 40 to 60% propylene glycol in water under occlusion (eg, a thin plastic film or bag worn overnight) every night after hydrating the skin (eg, by bathing or showering); in children, the preparation should be applied twice daily without occlusion. After scale has decreased, less frequent application is required. Other useful topical agents include ceramide-based creams, 6% salicylic acid gel, hydrophilic petrolatum and water (in equal parts), and the alpha-hydroxy acids in various bases. Topical calcipotriol cream has been used with success; however, this vitamin D derivative can result in hypercalcemia when used over broad areas, especially in small children.
Retinoids are effective in treating inherited ichthyosis. Oral synthetic retinoids are effective for most ichthyoses. Acitretin ( see Other systemic treatments Other systemic treatments 
) is effective in treating most forms of inherited ichthyosis. In lamellar ichthyosis, 0.1% tretinoin cream or oral isotretinoin may be effective. The lowest effective dose should be used. Long-term (1 year) treatment with oral isotretinoin has resulted in bony exostoses in some patients, and other long-term adverse effects may arise.
Infection prophylaxis
Patients with epidermolytic hyperkeratosis may need long-term treatment with cloxacillin 250 mg orally 3 or 4 times a day or erythromycin 250 mg orally 3 or 4 times a day, as long as thick intertriginous scale is present, to prevent bacterial superinfection from causing painful, foul-smelling pustules. Regularly using soaps containing chlorhexidine may also reduce the bacteria, but these soaps tend to dry the skin.
Treatment reference
1. Mazereeuw-Hautier J, Vahlquist A, Traupe H, et al: Management of congenital ichthyoses: European guidelines of care, part one. Br J Dermatol 180(2):272–281, 2019. doi: 10.1111/bjd.17203
Key Points
Ichthyosis may be acquired or inherited as an isolated disorder or as part of a syndrome.
Evaluate patients with gradual-onset ichthyosis for an underlying systemic disorder.
Emollients that speed the shedding of skin (keratolytics) are effective in treating ichthyosis.
