As in adults, nickel is the most common allergen in children [1, 4, 12]. Ear piercing and atopic dermatitis are regarded as major risk factors, and the frequency of nickel allergy is higher among girls. Exposure sources in children are numerous. Nickel sensitization may occur from the contact with jewelry, in particular earrings, metal buttons, zippers, hair clips, snaps, safety pins, jeans and belt buckles, metal accessories on shoes, coins, metal toys, medallions, magnets, keys, door handles, ballet balance bars, school chairs, etc. [4]. Orthodontic appliances containing nickel have occasionally been reported to cause cheilitis, perioral dermatitis, stomatitis [13], and even systemically induced dermatitis or more generalized reactions [14]. Cell phones, computers, and gaming devices have been observed as a new cause of nickel sensitization [15].

When testing infants and very young children with nickel, the risk of false-positive reactions should be kept in mind [16].

Cobalt sensitization is often found in association with nickel sensitization; thus, the exposure sources of the two allergens are similar. Other sources that may be relevant to children and especially adolescents are tattoo ink, makeup, nail lacquer, and leather [17].

The most common source of chromium allergy in children seems to be the leather. Especially leather shoes have been observed to cause chromium dermatitis in children.

The most important sources of aluminum exposure in children are aluminum-adsorbed vaccines. Aluminum allergy often presents as intensely itchy subcutaneous nodules at the injection site. The nodule may persist for months to years, whereas the itch normally fades, as does the aluminum allergy. In a Swedish study, the aluminum allergy was no longer detectable in two thirds of the children at follow-up of 5 years or later [18]. In another study of 40 children with aluminum allergy and vaccination granulomas, 25 later received a booster vaccination, and only two developed a new itching nodule [19].

Exposure to aluminum may also occur when children are hyposensitized to type I allergens with aluminum-containing extracts [18], or from treatment with aluminum-containing eardrops, toothpaste, antiperspirants, and other skin care products [20]. Usually, patch testing is performed using aluminum chloride hexahydrate 2 % in pet. and an empty Finn Chamber. However, if contact allergy to aluminum is suspected and the test is negative to 2 %, the aluminum chloride hexahydrate concentration may be increased to 10 % in pet [4].

Fragrance contact allergy is increasingly observed among children [1, 3], and even small children are exposed [8]. Exposure is usually due to perfumes, moisturizers, and deodorants. Scented products are ubiquitous, and the threshold for suspecting fragrance allergy as the possible cause of a child’s dermatitis should be low. Typical sites of involvement include areas of greatest contact, such as the face, the neck, and the axillae.

Preservatives are another common cause of contact allergy in children. In this context, methylisothiazolinone (MI) deserves special mentioning. It is a chemical preservative found in a variety of products used for children such as wet wipes, creams, liquid soaps, and shampoos. MI has recently received increased attention because of an alarming increase in the prevalence of contact allergy [6]. In addition to various cosmetics and skin care products, MI is used in the preservation of paint and can cause airborne dermatitis in individuals sensitized to the allergen [5].

Contact allergy to sunscreen ingredients should be considered, especially if a child presents with flares of dermatitis during spring or summer. Several sunscreen agents have been reported to cause contact allergy in children, including octocrylene, butyl methoxydibenzoylmethane, 2-ethylhexyl-4-methoxycinnamate, 4-methylbenzylidene camphor, and 4-isopropyl-dibenzoylmethane.